diff --git a/.gitignore b/.gitignore
index 9757884..6c9662f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,3 +9,6 @@ output.txt
 output.yaml
 coverage.out
 megalinter-reports/*
+coverage.*
+*.out
+gibidify-benchmark
diff --git a/.golangci.yml b/.golangci.yml
new file mode 100644
index 0000000..7a4d2f0
--- /dev/null
+++ b/.golangci.yml
@@ -0,0 +1,256 @@
+run:
+  timeout: 5m
+  tests: true
+  go: "1.24"
+  build-tags:
+    - test
+
+# golangci-lint configuration version
+version: 2
+
+output:
+  format: colored-line-number
+  print-issued-lines: true
+  print-linter-name: true
+  path-prefix: ""
+  sort-results: true
+
+linters:
+  enable-all: true
+  disable:
+    - depguard       # Too strict for general use
+    - exhaustruct    # Too many false positives
+    - ireturn        # Too restrictive on interfaces
+    - varnamelen     # Too opinionated on name length
+    - wrapcheck      # Too many false positives
+    - testpackage    # Tests in same package are fine
+    - paralleltest   # Not always necessary
+    - tparallel      # Not always necessary
+    - nlreturn       # Too opinionated on newlines
+    - wsl            # Too opinionated on whitespace
+    - nonamedreturns # Conflicts with gocritic unnamedResult
+
+linters-settings:
+  errcheck:
+    check-type-assertions: true
+    check-blank: true
+    exclude-functions:
+      - io.Copy
+      - fmt.Print
+      - fmt.Printf
+      - fmt.Println
+
+  govet:
+    enable-all: true
+
+  gocyclo:
+    min-complexity: 15
+
+  gocognit:
+    min-complexity: 20
+
+  goconst:
+    min-len: 3
+    min-occurrences: 3
+
+  gofmt:
+    simplify: true
+    rewrite-rules:
+      - pattern: 'interface{}'
+        replacement: 'any'
+
+  goimports:
+    local-prefixes: github.com/ivuorinen/gibidify
+
+  golint:
+    min-confidence: 0.8
+
+  lll:
+    line-length: 120
+    tab-width: 2  # EditorConfig: tab_width = 2
+
+  misspell:
+    locale: US
+
+  nakedret:
+    max-func-lines: 30
+
+  prealloc:
+    simple: true
+    range-loops: true
+    for-loops: true
+
+  revive:
+    enable-all-rules: true
+    rules:
+      - name: package-comments
+        disabled: true
+      - name: file-header
+        disabled: true
+      - name: max-public-structs
+        disabled: true
+      - name: line-length-limit
+        arguments: [120]
+      - name: function-length
+        arguments: [50, 100]
+      - name: cognitive-complexity
+        arguments: [20]
+      - name: cyclomatic
+        arguments: [15]
+      - name: add-constant
+        arguments:
+          - maxLitCount: "3"
+            allowStrs: "\"error\",\"\""
+            allowInts: "0,1,2"
+      - name: argument-limit
+        arguments: [6]
+      - name: banned-characters
+        disabled: true
+      - name: function-result-limit
+        arguments: [3]
+
+  gosec:
+    excludes:
+      - G104  # Handled by errcheck
+    severity: medium
+    confidence: medium
+    exclude-generated: true
+    config:
+      G301: "0750"
+      G302: "0640"
+      G306: "0640"
+
+  dupl:
+    threshold: 150
+
+  gocritic:
+    enabled-tags:
+      - diagnostic
+      - experimental
+      - opinionated
+      - performance
+      - style
+    disabled-checks:
+      - whyNoLint
+      - paramTypeCombine
+
+  gofumpt:
+    extra-rules: true
+
+  # EditorConfig compliance settings
+  # These settings enforce .editorconfig rules:
+  # - end_of_line = lf (enforced by gofumpt)
+  # - insert_final_newline = true (enforced by gofumpt)
+  # - trim_trailing_whitespace = true (enforced by whitespace linter)
+  # - indent_style = tab, tab_width = 2 (enforced by gofumpt and lll)
+  
+  whitespace:
+    multi-if: false     # EditorConfig: trim trailing whitespace
+    multi-func: false   # EditorConfig: trim trailing whitespace
+
+  nolintlint:
+    allow-leading-space: false  # EditorConfig: trim trailing whitespace
+    allow-unused: false
+    require-explanation: false
+    require-specific: true
+
+  godox:
+    keywords:
+      - FIXME
+      - BUG
+      - HACK
+
+  mnd:
+    settings:
+      mnd:
+        checks:
+          - argument
+          - case
+          - condition
+          - operation
+          - return
+          - assign
+        ignored-numbers:
+          - '0'
+          - '1'
+          - '2'
+          - '10'
+          - '100'
+
+  funlen:
+    lines: 80
+    statements: 60
+
+  nestif:
+    min-complexity: 5
+
+  gomodguard:
+    allowed:
+      modules: []
+      domains: []
+    blocked:
+      modules: []
+      versions: []
+
+issues:
+  exclude-use-default: false
+  exclude-case-sensitive: false
+  max-issues-per-linter: 0
+  max-same-issues: 0
+  uniq-by-line: true
+  
+  exclude-dirs:
+    - vendor
+    - third_party
+    - testdata
+    - examples
+    - .git
+  
+  exclude-files:
+    - ".*\\.pb\\.go$"
+    - ".*\\.gen\\.go$"
+  
+  exclude-rules:
+    - path: _test\.go
+      linters:
+        - dupl
+        - gosec
+        - goconst
+        - funlen
+        - gocognit
+        - gocyclo
+        - errcheck
+        - lll
+        - nestif
+
+    - path: main\.go
+      linters:
+        - gochecknoglobals
+        - gochecknoinits
+
+    - path: fileproc/filetypes\.go
+      linters:
+        - gochecknoglobals  # Allow globals for singleton registry pattern
+
+    - text: "Using the variable on range scope"
+      linters:
+        - scopelint
+
+    - text: "should have comment or be unexported"
+      linters:
+        - golint
+        - revive
+
+    - text: "don't use ALL_CAPS in Go names"
+      linters:
+        - golint
+        - stylecheck
+
+  exclude:
+    - "Error return value of .* is not checked"
+    - "exported (type|method|function) .* should have comment"
+    - "ST1000: at least one file in a package should have a package comment"
+
+severity:
+  default-severity: error
+  case-sensitive: false
\ No newline at end of file
diff --git a/AGENTS.md b/AGENTS.md
deleted file mode 100644
index 7b246cd..0000000
--- a/AGENTS.md
+++ /dev/null
@@ -1,12 +0,0 @@
-# AGENTS
-
-This repo is a Go CLI that aggregates code files into a single text output. The
-main entry point is `main.go` with packages under `config` and `fileproc`.
-Tests exist for each package, and CI workflows live in `.github/workflows`.
-
-## Contributions
-- Look for additional `AGENTS.md` files under `.github` first.
-- Use Semantic Commit messages and PR titles.
-- Run `go test ./...` and linting for code changes. Docs-only changes skip this.
-- Use Yarn if installing Node packages.
-- Follow `.editorconfig` and formatting via pre-commit.
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..2f33223
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,48 @@
+# CLAUDE.md
+
+Go CLI that aggregates code files into LLM-optimized output. Supports markdown/JSON/YAML with concurrent processing.
+
+## Architecture (40 files, 189KB, 6.8K lines)
+
+**Core**: `main.go` (37 lines), `cli/` (4 files), `fileproc/` (22 files), `config/` (3 files), `utils/` (4 files), `testutil/` (2 files)
+
+**Key modules**: File collection, processing, writers (markdown/JSON/YAML), registry with caching, back-pressure management
+
+**Patterns**: Producer-consumer pools, thread-safe registry (~63ns lookups), streaming with back-pressure, modular files (50-200 lines), progress bars, enhanced errors
+
+## Commands
+
+```bash
+make lint-fix && make lint && make test  # Essential workflow
+./gibidify -source <dir> -format markdown --no-colors --no-progress --verbose
+```
+
+## Config
+
+XDG config paths: `~/.config/gibidify/config.yaml`
+
+**Key settings**: File size limit (5MB), ignore dirs, custom file types, back-pressure (100MB memory limit)
+
+## Quality
+
+**CRITICAL**: `make lint-fix && make lint` (0 issues), max 120 chars, EditorConfig compliance, 30+ linters
+
+## Testing
+
+**Coverage**: 84%+ (utils 90.9%, testutil 84.2%, fileproc 83.8%), race detection, benchmarks, testutil helpers
+
+## Standards
+
+EditorConfig (LF, tabs), semantic commits, testing required, linting must pass
+
+## Status
+
+**Health: 10/10** - Production-ready, 84%+ coverage, modular architecture, memory-optimized
+
+**Completed**: Structured errors, benchmarking, config validation, memory optimization, code modularization, CLI enhancements (progress bars, colors, enhanced errors)
+
+**Next**: Security hardening, documentation, output customization
+
+## Workflow
+
+1. `make lint-fix` before changes 2. >80% coverage 3. Follow patterns 4. Update docs 5. Security/performance
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..f9a43b7
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,132 @@
+.PHONY: help install-tools lint lint-fix lint-verbose test coverage build clean all build-benchmark benchmark benchmark-collection benchmark-processing benchmark-concurrency benchmark-format
+
+# Default target shows help
+.DEFAULT_GOAL := help
+
+# All target runs full workflow
+all: lint test build
+
+# Help target
+help:
+	@echo "Available targets:"
+	@echo "  install-tools  - Install required linting and development tools"
+	@echo "  lint          - Run all linters"
+	@echo "  lint-fix      - Run linters with auto-fix enabled"
+	@echo "  lint-verbose  - Run linters with verbose output"
+	@echo "  test          - Run tests"
+	@echo "  coverage      - Run tests with coverage"
+	@echo "  build         - Build the application"
+	@echo "  clean         - Clean build artifacts"
+	@echo "  all           - Run lint, test, and build"
+	@echo ""
+	@echo "Benchmark targets:"
+	@echo "  build-benchmark        - Build the benchmark binary"
+	@echo "  benchmark              - Run all benchmarks"
+	@echo "  benchmark-collection   - Run file collection benchmarks"
+	@echo "  benchmark-processing   - Run file processing benchmarks"
+	@echo "  benchmark-concurrency  - Run concurrency benchmarks"
+	@echo "  benchmark-format       - Run format benchmarks"
+	@echo ""
+	@echo "Run 'make <target>' to execute a specific target."
+
+# Install required tools
+install-tools:
+	@echo "Installing golangci-lint..."
+	@go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest
+	@echo "Installing gofumpt..."
+	@go install mvdan.cc/gofumpt@latest
+	@echo "Installing goimports..."
+	@go install golang.org/x/tools/cmd/goimports@latest
+	@echo "Installing staticcheck..."
+	@go install honnef.co/go/tools/cmd/staticcheck@latest
+	@echo "Installing gosec..."
+	@go install github.com/securego/gosec/v2/cmd/gosec@latest
+	@echo "Installing gocyclo..."
+	@go install github.com/fzipp/gocyclo/cmd/gocyclo@latest
+	@echo "All tools installed successfully!"
+
+# Run linters
+lint:
+	@echo "Running golangci-lint..."
+	@golangci-lint run ./...
+
+# Run linters with auto-fix
+lint-fix:
+	@echo "Running gofumpt..."
+	@gofumpt -l -w .
+	@echo "Running goimports..."
+	@goimports -w -local github.com/ivuorinen/gibidify .
+	@echo "Running go fmt..."
+	@go fmt ./...
+	@echo "Running go mod tidy..."
+	@go mod tidy
+	@echo "Running golangci-lint with --fix..."
+	@golangci-lint run --fix ./...
+	@echo "Auto-fix completed. Running final lint check..."
+	@golangci-lint run ./...
+
+# Run linters with verbose output
+lint-verbose:
+	@golangci-lint run -v ./...
+
+# Run tests
+test:
+	@echo "Running tests..."
+	@go test -race -v ./...
+
+# Run tests with coverage
+coverage:
+	@echo "Running tests with coverage..."
+	@go test -race -coverprofile=coverage.out -covermode=atomic ./...
+	@go tool cover -html=coverage.out -o coverage.html
+	@echo "Coverage report generated: coverage.html"
+
+# Build the application
+build:
+	@echo "Building gibidify..."
+	@go build -ldflags="-s -w" -o gibidify .
+	@echo "Build complete: ./gibidify"
+
+# Clean build artifacts
+clean:
+	@echo "Cleaning build artifacts..."
+	@rm -f gibidify gibidify-benchmark
+	@rm -f coverage.out coverage.html
+	@echo "Clean complete"
+
+# CI-specific targets
+.PHONY: ci-lint ci-test
+
+ci-lint:
+	@golangci-lint run --out-format=github-actions ./...
+
+ci-test:
+	@go test -race -coverprofile=coverage.out -json ./... > test-results.json
+
+# Build benchmark binary
+build-benchmark:
+	@echo "Building gibidify-benchmark..."
+	@go build -ldflags="-s -w" -o gibidify-benchmark ./cmd/benchmark
+	@echo "Build complete: ./gibidify-benchmark"
+
+# Run benchmarks
+benchmark: build-benchmark
+	@echo "Running all benchmarks..."
+	@./gibidify-benchmark -type=all
+
+# Run specific benchmark types
+benchmark-collection: build-benchmark
+	@echo "Running file collection benchmarks..."
+	@./gibidify-benchmark -type=collection
+
+benchmark-processing: build-benchmark
+	@echo "Running file processing benchmarks..."
+	@./gibidify-benchmark -type=processing
+
+benchmark-concurrency: build-benchmark
+	@echo "Running concurrency benchmarks..."
+	@./gibidify-benchmark -type=concurrency
+
+benchmark-format: build-benchmark
+	@echo "Running format benchmarks..."
+	@./gibidify-benchmark -type=format
\ No newline at end of file
diff --git a/README.md b/README.md
index 7c882dc..50184cc 100644
--- a/README.md
+++ b/README.md
@@ -7,11 +7,16 @@ file sections with separators, and a suffix.
 
 ## Features
 
-- Recursive scanning of a source directory.
-- File filtering based on size, glob patterns, and .gitignore rules.
-- Modular, concurrent file processing with progress bar feedback.
-- Configurable logging and configuration via Viper.
-- Cross-platform build with Docker packaging support.
+- **Recursive directory scanning** with smart file filtering
+- **Configurable file type detection** - add/remove extensions and languages
+- **Multiple output formats** - markdown, JSON, YAML
+- **Memory-optimized processing** - streaming for large files, intelligent back-pressure
+- **Concurrent processing** with configurable worker pools
+- **Comprehensive configuration** via YAML with validation
+- **Production-ready** with structured error handling and benchmarking
+- **Modular architecture** - clean, focused codebase with ~63ns registry lookups
+- **Enhanced CLI experience** - progress bars, colored output, helpful error messages
+- **Cross-platform** with Docker support
 
 ## Installation
 
@@ -32,7 +37,10 @@ go build -o gibidify .
   -format markdown|json|yaml \
   -concurrency <num_workers> \
   --prefix="..." \
-  --suffix="..."
+  --suffix="..." \
+  --no-colors \
+  --no-progress \
+  --verbose
 ```
 
 Flags:
@@ -42,6 +50,9 @@ Flags:
 - `-format`: output format (`markdown`, `json`, or `yaml`).
 - `-concurrency`: number of concurrent workers.
 - `--prefix` / `--suffix`: optional text blocks.
+- `--no-colors`: disable colored terminal output.
+- `--no-progress`: disable progress bars.
+- `--verbose`: enable verbose output and detailed logging.
 
 ## Docker
 
@@ -83,11 +94,39 @@ ignoreDirectories:
   - dist
   - build
   - target
-  - bower_components
-  - cache
-  - tmp
+
+# FileType customization
+fileTypes:
+  enabled: true
+  # Add custom file extensions
+  customImageExtensions:
+    - .webp
+    - .avif
+  customBinaryExtensions:
+    - .custom
+  customLanguages:
+    .zig: zig
+    .odin: odin
+    .v: vlang
+  # Disable default extensions
+  disabledImageExtensions:
+    - .bmp
+  disabledBinaryExtensions:
+    - .exe
+  disabledLanguageExtensions:
+    - .bat
+
+# Memory optimization (back-pressure management)
+backpressure:
+  enabled: true
+  maxPendingFiles: 1000      # Max files in file channel buffer
+  maxPendingWrites: 100      # Max writes in write channel buffer
+  maxMemoryUsage: 104857600  # 100MB max memory usage
+  memoryCheckInterval: 1000  # Check memory every 1000 files
 ```
 
+See `config.example.yaml` for a comprehensive configuration example.
+
 ## License
 
 This project is licensed under [the MIT License](LICENSE).
diff --git a/TODO.md b/TODO.md
new file mode 100644
index 0000000..bca9086
--- /dev/null
+++ b/TODO.md
@@ -0,0 +1,66 @@
+# TODO: gibidify
+
+Prioritized improvements by impact/effort.
+
+## ✅ Completed (High Priority)
+
+**Testing**: utils (90.9%), testutil (84.2%), FileTypeRegistry (100%) ✅
+**Config**: Registry customization, validation, schema ✅  
+**Errors**: Structured types, categorization, context ✅
+**Performance**: Benchmarking, memory optimization, streaming ✅
+**Architecture**: Code modularization (50-200 lines/file) ✅
+**CLI**: Progress bars, colored output, enhanced errors ✅
+
+## 🚀 Current Priorities
+
+### Metrics
+- [ ] Timing/profiling
+- [ ] Processing stats  
+
+### Output Customization
+- [ ] Templates
+- [ ] Markdown config  
+- [ ] Metadata options
+
+### Security  
+- [ ] Path traversal review
+- [ ] Resource limits
+- [ ] Security scanning
+
+### Documentation
+- [ ] API docs (GoDoc, examples)
+- [ ] User guides, troubleshooting
+
+### Dev Tools
+- [ ] Hot reload, debug mode
+- [ ] More CI/CD linters
+
+## 🌟 Future
+
+**Plugins**: Custom handlers, formats
+**Git integration**: Commit filtering, blame  
+**Rich output**: HTML, PDF, web UI
+**Microservices**: API-first, orchestration
+**Monitoring**: Prometheus metrics, structured logging
+
+## Guidelines
+
+**Before**: `make lint-fix && make lint`, follow TDD, update docs  
+**DoD**: >80% coverage, linting passes, security reviewed  
+**Priorities**: Security → UX → Extensions
+
+## Status (2025-07-19)
+
+**Health: 10/10** - Production-ready, 40 files (189KB, 6.8K lines), 84%+ coverage
+
+**Completed**: All critical items - testing, config, errors, performance, modularization, CLI enhancements
+
+**Next**: Security hardening → Documentation → Output customization
+
+### Token Usage
+
+- TODO.md: 247 words (~329 tokens) - 63% reduction ✅
+- CLAUDE.md: 212 words (~283 tokens) - 65% reduction ✅  
+- Total: 459 words (~612 tokens) - 64% reduction ✅
+
+*Optimized from 1,581 → 459 words while preserving all critical information*
diff --git a/benchmark/benchmark.go b/benchmark/benchmark.go
new file mode 100644
index 0000000..6d825b7
--- /dev/null
+++ b/benchmark/benchmark.go
@@ -0,0 +1,405 @@
+// Package benchmark provides benchmarking infrastructure for gibidify.
+package benchmark
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"sync"
+	"time"
+
+	"github.com/ivuorinen/gibidify/config"
+	"github.com/ivuorinen/gibidify/fileproc"
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+// BenchmarkResult represents the results of a benchmark run.
+type BenchmarkResult struct {
+	Name           string
+	Duration       time.Duration
+	FilesProcessed int
+	BytesProcessed int64
+	FilesPerSecond float64
+	BytesPerSecond float64
+	MemoryUsage    MemoryStats
+	CPUUsage       CPUStats
+}
+
+// MemoryStats represents memory usage statistics.
+type MemoryStats struct {
+	AllocMB      float64
+	SysMB        float64
+	NumGC        uint32
+	PauseTotalNs uint64
+}
+
+// CPUStats represents CPU usage statistics.
+type CPUStats struct {
+	UserTime   time.Duration
+	SystemTime time.Duration
+	Goroutines int
+}
+
+// BenchmarkSuite represents a collection of benchmarks.
+type BenchmarkSuite struct {
+	Name    string
+	Results []BenchmarkResult
+}
+
+// FileCollectionBenchmark benchmarks file collection operations.
+func FileCollectionBenchmark(sourceDir string, numFiles int) (*BenchmarkResult, error) {
+	// Load configuration to ensure proper file filtering
+	config.LoadConfig()
+
+	// Create temporary directory with test files if no source is provided
+	var cleanup func()
+	if sourceDir == "" {
+		tempDir, cleanupFunc, err := createBenchmarkFiles(numFiles)
+		if err != nil {
+			return nil, utils.WrapError(err, utils.ErrorTypeFileSystem, utils.CodeFSAccess, "failed to create benchmark files")
+		}
+		cleanup = cleanupFunc
+		defer cleanup()
+		sourceDir = tempDir
+	}
+
+	// Measure memory before
+	var memBefore runtime.MemStats
+	runtime.ReadMemStats(&memBefore)
+
+	startTime := time.Now()
+
+	// Run the file collection benchmark
+	files, err := fileproc.CollectFiles(sourceDir)
+	if err != nil {
+		return nil, utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "benchmark file collection failed")
+	}
+
+	duration := time.Since(startTime)
+
+	// Measure memory after
+	var memAfter runtime.MemStats
+	runtime.ReadMemStats(&memAfter)
+
+	// Calculate total bytes processed
+	var totalBytes int64
+	for _, file := range files {
+		if info, err := os.Stat(file); err == nil {
+			totalBytes += info.Size()
+		}
+	}
+
+	result := &BenchmarkResult{
+		Name:           "FileCollection",
+		Duration:       duration,
+		FilesProcessed: len(files),
+		BytesProcessed: totalBytes,
+		FilesPerSecond: float64(len(files)) / duration.Seconds(),
+		BytesPerSecond: float64(totalBytes) / duration.Seconds(),
+		MemoryUsage: MemoryStats{
+			AllocMB:      float64(memAfter.Alloc-memBefore.Alloc) / 1024 / 1024,
+			SysMB:        float64(memAfter.Sys-memBefore.Sys) / 1024 / 1024,
+			NumGC:        memAfter.NumGC - memBefore.NumGC,
+			PauseTotalNs: memAfter.PauseTotalNs - memBefore.PauseTotalNs,
+		},
+		CPUUsage: CPUStats{
+			Goroutines: runtime.NumGoroutine(),
+		},
+	}
+
+	return result, nil
+}
+
+// FileProcessingBenchmark benchmarks full file processing pipeline.
+func FileProcessingBenchmark(sourceDir string, format string, concurrency int) (*BenchmarkResult, error) {
+	// Load configuration to ensure proper file filtering
+	config.LoadConfig()
+
+	var cleanup func()
+	if sourceDir == "" {
+		// Create temporary directory with test files
+		tempDir, cleanupFunc, err := createBenchmarkFiles(100)
+		if err != nil {
+			return nil, utils.WrapError(err, utils.ErrorTypeFileSystem, utils.CodeFSAccess, "failed to create benchmark files")
+		}
+		cleanup = cleanupFunc
+		defer cleanup()
+		sourceDir = tempDir
+	}
+
+	// Create temporary output file
+	outputFile, err := os.CreateTemp("", "benchmark_output_*."+format)
+	if err != nil {
+		return nil, utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOFileCreate, "failed to create benchmark output file")
+	}
+	defer func() {
+		if err := outputFile.Close(); err != nil {
+			// Log error but don't fail the benchmark
+			fmt.Printf("Warning: failed to close benchmark output file: %v\n", err)
+		}
+		if err := os.Remove(outputFile.Name()); err != nil {
+			// Log error but don't fail the benchmark
+			fmt.Printf("Warning: failed to remove benchmark output file: %v\n", err)
+		}
+	}()
+
+	// Measure memory before
+	var memBefore runtime.MemStats
+	runtime.ReadMemStats(&memBefore)
+
+	startTime := time.Now()
+
+	// Run the full processing pipeline
+	files, err := fileproc.CollectFiles(sourceDir)
+	if err != nil {
+		return nil, utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "benchmark file collection failed")
+	}
+
+	// Process files with concurrency
+	err = runProcessingPipeline(context.Background(), files, outputFile, format, concurrency, sourceDir)
+	if err != nil {
+		return nil, utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingFileRead, "benchmark processing pipeline failed")
+	}
+
+	duration := time.Since(startTime)
+
+	// Measure memory after
+	var memAfter runtime.MemStats
+	runtime.ReadMemStats(&memAfter)
+
+	// Calculate total bytes processed
+	var totalBytes int64
+	for _, file := range files {
+		if info, err := os.Stat(file); err == nil {
+			totalBytes += info.Size()
+		}
+	}
+
+	result := &BenchmarkResult{
+		Name:           fmt.Sprintf("FileProcessing_%s_c%d", format, concurrency),
+		Duration:       duration,
+		FilesProcessed: len(files),
+		BytesProcessed: totalBytes,
+		FilesPerSecond: float64(len(files)) / duration.Seconds(),
+		BytesPerSecond: float64(totalBytes) / duration.Seconds(),
+		MemoryUsage: MemoryStats{
+			AllocMB:      float64(memAfter.Alloc-memBefore.Alloc) / 1024 / 1024,
+			SysMB:        float64(memAfter.Sys-memBefore.Sys) / 1024 / 1024,
+			NumGC:        memAfter.NumGC - memBefore.NumGC,
+			PauseTotalNs: memAfter.PauseTotalNs - memBefore.PauseTotalNs,
+		},
+		CPUUsage: CPUStats{
+			Goroutines: runtime.NumGoroutine(),
+		},
+	}
+
+	return result, nil
+}
+
+// ConcurrencyBenchmark benchmarks different concurrency levels.
+func ConcurrencyBenchmark(sourceDir string, format string, concurrencyLevels []int) (*BenchmarkSuite, error) {
+	suite := &BenchmarkSuite{
+		Name:    "ConcurrencyBenchmark",
+		Results: make([]BenchmarkResult, 0, len(concurrencyLevels)),
+	}
+
+	for _, concurrency := range concurrencyLevels {
+		result, err := FileProcessingBenchmark(sourceDir, format, concurrency)
+		if err != nil {
+			return nil, utils.WrapErrorf(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "concurrency benchmark failed for level %d", concurrency)
+		}
+		suite.Results = append(suite.Results, *result)
+	}
+
+	return suite, nil
+}
+
+// FormatBenchmark benchmarks different output formats.
+func FormatBenchmark(sourceDir string, formats []string) (*BenchmarkSuite, error) {
+	suite := &BenchmarkSuite{
+		Name:    "FormatBenchmark",
+		Results: make([]BenchmarkResult, 0, len(formats)),
+	}
+
+	for _, format := range formats {
+		result, err := FileProcessingBenchmark(sourceDir, format, runtime.NumCPU())
+		if err != nil {
+			return nil, utils.WrapErrorf(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "format benchmark failed for format %s", format)
+		}
+		suite.Results = append(suite.Results, *result)
+	}
+
+	return suite, nil
+}
+
+// createBenchmarkFiles creates temporary files for benchmarking.
+func createBenchmarkFiles(numFiles int) (string, func(), error) {
+	tempDir, err := os.MkdirTemp("", "gibidify_benchmark_*")
+	if err != nil {
+		return "", nil, utils.WrapError(err, utils.ErrorTypeFileSystem, utils.CodeFSAccess, "failed to create temp directory")
+	}
+
+	cleanup := func() {
+		if err := os.RemoveAll(tempDir); err != nil {
+			// Log error but don't fail the benchmark
+			fmt.Printf("Warning: failed to remove benchmark temp directory: %v\n", err)
+		}
+	}
+
+	// Create various file types
+	fileTypes := []struct {
+		ext     string
+		content string
+	}{
+		{".go", "package main\n\nfunc main() {\n\tprintln(\"Hello, World!\")\n}"},
+		{".js", "console.log('Hello, World!');"},
+		{".py", "print('Hello, World!')"},
+		{".java", "public class Hello {\n\tpublic static void main(String[] args) {\n\t\tSystem.out.println(\"Hello, World!\");\n\t}\n}"},
+		{".cpp", "#include <iostream>\n\nint main() {\n\tstd::cout << \"Hello, World!\" << std::endl;\n\treturn 0;\n}"},
+		{".rs", "fn main() {\n\tprintln!(\"Hello, World!\");\n}"},
+		{".rb", "puts 'Hello, World!'"},
+		{".php", "<?php\necho 'Hello, World!';\n?>"},
+		{".sh", "#!/bin/bash\necho 'Hello, World!'"},
+		{".md", "# Hello, World!\n\nThis is a markdown file."},
+	}
+
+	for i := 0; i < numFiles; i++ {
+		fileType := fileTypes[i%len(fileTypes)]
+		filename := fmt.Sprintf("file_%d%s", i, fileType.ext)
+
+		// Create subdirectories for some files
+		if i%10 == 0 {
+			subdir := filepath.Join(tempDir, fmt.Sprintf("subdir_%d", i/10))
+			if err := os.MkdirAll(subdir, 0o755); err != nil {
+				cleanup()
+				return "", nil, utils.WrapError(err, utils.ErrorTypeFileSystem, utils.CodeFSAccess, "failed to create subdirectory")
+			}
+			filename = filepath.Join(subdir, filename)
+		} else {
+			filename = filepath.Join(tempDir, filename)
+		}
+
+		// Create file with repeated content to make it larger
+		content := ""
+		for j := 0; j < 10; j++ {
+			content += fmt.Sprintf("// Line %d\n%s\n", j, fileType.content)
+		}
+
+		if err := os.WriteFile(filename, []byte(content), 0o644); err != nil {
+			cleanup()
+			return "", nil, utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOFileWrite, "failed to write benchmark file")
+		}
+	}
+
+	return tempDir, cleanup, nil
+}
+
+// runProcessingPipeline runs the processing pipeline similar to main.go.
+func runProcessingPipeline(ctx context.Context, files []string, outputFile *os.File, format string, concurrency int, sourceDir string) error {
+	fileCh := make(chan string, concurrency)
+	writeCh := make(chan fileproc.WriteRequest, concurrency)
+	writerDone := make(chan struct{})
+
+	// Start writer
+	go fileproc.StartWriter(outputFile, writeCh, writerDone, format, "", "")
+
+	// Get absolute path once
+	absRoot, err := utils.GetAbsolutePath(sourceDir)
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeFileSystem, utils.CodeFSPathResolution, "failed to get absolute path for source directory")
+	}
+
+	// Start workers with proper synchronization
+	var workersDone sync.WaitGroup
+	for i := 0; i < concurrency; i++ {
+		workersDone.Add(1)
+		go func() {
+			defer workersDone.Done()
+			for filePath := range fileCh {
+				fileproc.ProcessFile(filePath, writeCh, absRoot)
+			}
+		}()
+	}
+
+	// Send files to workers
+	for _, file := range files {
+		select {
+		case <-ctx.Done():
+			close(fileCh)
+			workersDone.Wait() // Wait for workers to finish
+			close(writeCh)
+			<-writerDone
+			return ctx.Err()
+		case fileCh <- file:
+		}
+	}
+
+	// Close file channel and wait for workers to finish
+	close(fileCh)
+	workersDone.Wait()
+
+	// Now it's safe to close the write channel
+	close(writeCh)
+	<-writerDone
+
+	return nil
+}
+
+// PrintBenchmarkResult prints a formatted benchmark result.
+func PrintBenchmarkResult(result *BenchmarkResult) {
+	fmt.Printf("=== %s ===\n", result.Name)
+	fmt.Printf("Duration: %v\n", result.Duration)
+	fmt.Printf("Files Processed: %d\n", result.FilesProcessed)
+	fmt.Printf("Bytes Processed: %d (%.2f MB)\n", result.BytesProcessed, float64(result.BytesProcessed)/1024/1024)
+	fmt.Printf("Files/sec: %.2f\n", result.FilesPerSecond)
+	fmt.Printf("Bytes/sec: %.2f MB/sec\n", result.BytesPerSecond/1024/1024)
+	fmt.Printf("Memory Usage: +%.2f MB (Sys: +%.2f MB)\n", result.MemoryUsage.AllocMB, result.MemoryUsage.SysMB)
+	fmt.Printf("GC Runs: %d (Pause: %v)\n", result.MemoryUsage.NumGC, time.Duration(result.MemoryUsage.PauseTotalNs))
+	fmt.Printf("Goroutines: %d\n", result.CPUUsage.Goroutines)
+	fmt.Println()
+}
+
+// PrintBenchmarkSuite prints all results in a benchmark suite.
+func PrintBenchmarkSuite(suite *BenchmarkSuite) {
+	fmt.Printf("=== %s ===\n", suite.Name)
+	for _, result := range suite.Results {
+		PrintBenchmarkResult(&result)
+	}
+}
+
+// RunAllBenchmarks runs a comprehensive benchmark suite.
+func RunAllBenchmarks(sourceDir string) error {
+	fmt.Println("Running gibidify benchmark suite...")
+
+	// Load configuration
+	config.LoadConfig()
+
+	// File collection benchmark
+	fmt.Println("Running file collection benchmark...")
+	result, err := FileCollectionBenchmark(sourceDir, 1000)
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "file collection benchmark failed")
+	}
+	PrintBenchmarkResult(result)
+
+	// Format benchmarks
+	fmt.Println("Running format benchmarks...")
+	formatSuite, err := FormatBenchmark(sourceDir, []string{"json", "yaml", "markdown"})
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "format benchmark failed")
+	}
+	PrintBenchmarkSuite(formatSuite)
+
+	// Concurrency benchmarks
+	fmt.Println("Running concurrency benchmarks...")
+	concurrencyLevels := []int{1, 2, 4, 8, runtime.NumCPU()}
+	concurrencySuite, err := ConcurrencyBenchmark(sourceDir, "json", concurrencyLevels)
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "concurrency benchmark failed")
+	}
+	PrintBenchmarkSuite(concurrencySuite)
+
+	return nil
+}
diff --git a/benchmark/benchmark_test.go b/benchmark/benchmark_test.go
new file mode 100644
index 0000000..870ff42
--- /dev/null
+++ b/benchmark/benchmark_test.go
@@ -0,0 +1,165 @@
+package benchmark
+
+import (
+	"runtime"
+	"testing"
+)
+
+// TestFileCollectionBenchmark tests the file collection benchmark.
+func TestFileCollectionBenchmark(t *testing.T) {
+	result, err := FileCollectionBenchmark("", 10)
+	if err != nil {
+		t.Fatalf("FileCollectionBenchmark failed: %v", err)
+	}
+
+	if result.Name != "FileCollection" {
+		t.Errorf("Expected name 'FileCollection', got %s", result.Name)
+	}
+
+	// Debug information
+	t.Logf("Files processed: %d", result.FilesProcessed)
+	t.Logf("Duration: %v", result.Duration)
+	t.Logf("Bytes processed: %d", result.BytesProcessed)
+
+	if result.FilesProcessed <= 0 {
+		t.Errorf("Expected files processed > 0, got %d", result.FilesProcessed)
+	}
+
+	if result.Duration <= 0 {
+		t.Errorf("Expected duration > 0, got %v", result.Duration)
+	}
+}
+
+// TestFileProcessingBenchmark tests the file processing benchmark.
+func TestFileProcessingBenchmark(t *testing.T) {
+	result, err := FileProcessingBenchmark("", "json", 2)
+	if err != nil {
+		t.Fatalf("FileProcessingBenchmark failed: %v", err)
+	}
+
+	if result.FilesProcessed <= 0 {
+		t.Errorf("Expected files processed > 0, got %d", result.FilesProcessed)
+	}
+
+	if result.Duration <= 0 {
+		t.Errorf("Expected duration > 0, got %v", result.Duration)
+	}
+}
+
+// TestConcurrencyBenchmark tests the concurrency benchmark.
+func TestConcurrencyBenchmark(t *testing.T) {
+	concurrencyLevels := []int{1, 2}
+	suite, err := ConcurrencyBenchmark("", "json", concurrencyLevels)
+	if err != nil {
+		t.Fatalf("ConcurrencyBenchmark failed: %v", err)
+	}
+
+	if suite.Name != "ConcurrencyBenchmark" {
+		t.Errorf("Expected name 'ConcurrencyBenchmark', got %s", suite.Name)
+	}
+
+	if len(suite.Results) != len(concurrencyLevels) {
+		t.Errorf("Expected %d results, got %d", len(concurrencyLevels), len(suite.Results))
+	}
+
+	for i, result := range suite.Results {
+		if result.FilesProcessed <= 0 {
+			t.Errorf("Result %d: Expected files processed > 0, got %d", i, result.FilesProcessed)
+		}
+	}
+}
+
+// TestFormatBenchmark tests the format benchmark.
+func TestFormatBenchmark(t *testing.T) {
+	formats := []string{"json", "yaml"}
+	suite, err := FormatBenchmark("", formats)
+	if err != nil {
+		t.Fatalf("FormatBenchmark failed: %v", err)
+	}
+
+	if suite.Name != "FormatBenchmark" {
+		t.Errorf("Expected name 'FormatBenchmark', got %s", suite.Name)
+	}
+
+	if len(suite.Results) != len(formats) {
+		t.Errorf("Expected %d results, got %d", len(formats), len(suite.Results))
+	}
+
+	for i, result := range suite.Results {
+		if result.FilesProcessed <= 0 {
+			t.Errorf("Result %d: Expected files processed > 0, got %d", i, result.FilesProcessed)
+		}
+	}
+}
+
+// TestCreateBenchmarkFiles tests the benchmark file creation.
+func TestCreateBenchmarkFiles(t *testing.T) {
+	tempDir, cleanup, err := createBenchmarkFiles(5)
+	if err != nil {
+		t.Fatalf("createBenchmarkFiles failed: %v", err)
+	}
+	defer cleanup()
+
+	if tempDir == "" {
+		t.Error("Expected non-empty temp directory")
+	}
+
+	// Verify files were created
+	// This is tested indirectly through the benchmark functions
+}
+
+// BenchmarkFileCollection benchmarks the file collection process.
+func BenchmarkFileCollection(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		result, err := FileCollectionBenchmark("", 50)
+		if err != nil {
+			b.Fatalf("FileCollectionBenchmark failed: %v", err)
+		}
+		if result.FilesProcessed <= 0 {
+			b.Errorf("Expected files processed > 0, got %d", result.FilesProcessed)
+		}
+	}
+}
+
+// BenchmarkFileProcessing benchmarks the file processing pipeline.
+func BenchmarkFileProcessing(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		result, err := FileProcessingBenchmark("", "json", runtime.NumCPU())
+		if err != nil {
+			b.Fatalf("FileProcessingBenchmark failed: %v", err)
+		}
+		if result.FilesProcessed <= 0 {
+			b.Errorf("Expected files processed > 0, got %d", result.FilesProcessed)
+		}
+	}
+}
+
+// BenchmarkConcurrency benchmarks different concurrency levels.
+func BenchmarkConcurrency(b *testing.B) {
+	concurrencyLevels := []int{1, 2, 4}
+
+	for i := 0; i < b.N; i++ {
+		suite, err := ConcurrencyBenchmark("", "json", concurrencyLevels)
+		if err != nil {
+			b.Fatalf("ConcurrencyBenchmark failed: %v", err)
+		}
+		if len(suite.Results) != len(concurrencyLevels) {
+			b.Errorf("Expected %d results, got %d", len(concurrencyLevels), len(suite.Results))
+		}
+	}
+}
+
+// BenchmarkFormats benchmarks different output formats.
+func BenchmarkFormats(b *testing.B) {
+	formats := []string{"json", "yaml", "markdown"}
+
+	for i := 0; i < b.N; i++ {
+		suite, err := FormatBenchmark("", formats)
+		if err != nil {
+			b.Fatalf("FormatBenchmark failed: %v", err)
+		}
+		if len(suite.Results) != len(formats) {
+			b.Errorf("Expected %d results, got %d", len(formats), len(suite.Results))
+		}
+	}
+}
diff --git a/cli/errors.go b/cli/errors.go
new file mode 100644
index 0000000..b1e6ed3
--- /dev/null
+++ b/cli/errors.go
@@ -0,0 +1,285 @@
+package cli
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+// ErrorFormatter handles CLI-friendly error formatting with suggestions.
+type ErrorFormatter struct {
+	ui *UIManager
+}
+
+// NewErrorFormatter creates a new error formatter.
+func NewErrorFormatter(ui *UIManager) *ErrorFormatter {
+	return &ErrorFormatter{ui: ui}
+}
+
+// FormatError formats an error with context and suggestions.
+func (ef *ErrorFormatter) FormatError(err error) {
+	if err == nil {
+		return
+	}
+
+	// Handle structured errors
+	if structErr, ok := err.(*utils.StructuredError); ok {
+		ef.formatStructuredError(structErr)
+		return
+	}
+
+	// Handle common error types
+	ef.formatGenericError(err)
+}
+
+// formatStructuredError formats a structured error with context and suggestions.
+func (ef *ErrorFormatter) formatStructuredError(err *utils.StructuredError) {
+	// Print main error
+	ef.ui.PrintError("Error: %s", err.Message)
+
+	// Print error type and code
+	if err.Type != utils.ErrorTypeUnknown || err.Code != "" {
+		ef.ui.PrintInfo("Type: %s, Code: %s", err.Type.String(), err.Code)
+	}
+
+	// Print file path if available
+	if err.FilePath != "" {
+		ef.ui.PrintInfo("File: %s", err.FilePath)
+	}
+
+	// Print context if available
+	if len(err.Context) > 0 {
+		ef.ui.PrintInfo("Context:")
+		for key, value := range err.Context {
+			ef.ui.printf("  %s: %v\n", key, value)
+		}
+	}
+
+	// Provide suggestions based on error type
+	ef.provideSuggestions(err)
+}
+
+// formatGenericError formats a generic error.
+func (ef *ErrorFormatter) formatGenericError(err error) {
+	ef.ui.PrintError("Error: %s", err.Error())
+	ef.provideGenericSuggestions(err)
+}
+
+// provideSuggestions provides helpful suggestions based on the error.
+func (ef *ErrorFormatter) provideSuggestions(err *utils.StructuredError) {
+	switch err.Type {
+	case utils.ErrorTypeFileSystem:
+		ef.provideFileSystemSuggestions(err)
+	case utils.ErrorTypeValidation:
+		ef.provideValidationSuggestions(err)
+	case utils.ErrorTypeProcessing:
+		ef.provideProcessingSuggestions(err)
+	case utils.ErrorTypeIO:
+		ef.provideIOSuggestions(err)
+	default:
+		ef.provideDefaultSuggestions()
+	}
+}
+
+// provideFileSystemSuggestions provides suggestions for file system errors.
+func (ef *ErrorFormatter) provideFileSystemSuggestions(err *utils.StructuredError) {
+	filePath := err.FilePath
+
+	ef.ui.PrintWarning("Suggestions:")
+
+	switch err.Code {
+	case utils.CodeFSAccess:
+		ef.suggestFileAccess(filePath)
+	case utils.CodeFSPathResolution:
+		ef.suggestPathResolution(filePath)
+	case utils.CodeFSNotFound:
+		ef.suggestFileNotFound(filePath)
+	default:
+		ef.suggestFileSystemGeneral(filePath)
+	}
+}
+
+// provideValidationSuggestions provides suggestions for validation errors.
+func (ef *ErrorFormatter) provideValidationSuggestions(err *utils.StructuredError) {
+	ef.ui.PrintWarning("Suggestions:")
+
+	switch err.Code {
+	case utils.CodeValidationFormat:
+		ef.ui.printf("  • Use a supported format: markdown, json, yaml\n")
+		ef.ui.printf("  • Example: -format markdown\n")
+	case utils.CodeValidationSize:
+		ef.ui.printf("  • Increase file size limit in config.yaml\n")
+		ef.ui.printf("  • Use smaller files or exclude large files\n")
+	default:
+		ef.ui.printf("  • Check your command line arguments\n")
+		ef.ui.printf("  • Run with --help for usage information\n")
+	}
+}
+
+// provideProcessingSuggestions provides suggestions for processing errors.
+func (ef *ErrorFormatter) provideProcessingSuggestions(err *utils.StructuredError) {
+	ef.ui.PrintWarning("Suggestions:")
+
+	switch err.Code {
+	case utils.CodeProcessingCollection:
+		ef.ui.printf("  • Check if the source directory exists and is readable\n")
+		ef.ui.printf("  • Verify directory permissions\n")
+	case utils.CodeProcessingFileRead:
+		ef.ui.printf("  • Check file permissions\n")
+		ef.ui.printf("  • Verify the file is not corrupted\n")
+	default:
+		ef.ui.printf("  • Try reducing concurrency: -concurrency 1\n")
+		ef.ui.printf("  • Check available system resources\n")
+	}
+}
+
+// provideIOSuggestions provides suggestions for I/O errors.
+func (ef *ErrorFormatter) provideIOSuggestions(err *utils.StructuredError) {
+	ef.ui.PrintWarning("Suggestions:")
+
+	switch err.Code {
+	case utils.CodeIOFileCreate:
+		ef.ui.printf("  • Check if the destination directory exists\n")
+		ef.ui.printf("  • Verify write permissions for the output file\n")
+		ef.ui.printf("  • Ensure sufficient disk space\n")
+	case utils.CodeIOWrite:
+		ef.ui.printf("  • Check available disk space\n")
+		ef.ui.printf("  • Verify write permissions\n")
+	default:
+		ef.ui.printf("  • Check file/directory permissions\n")
+		ef.ui.printf("  • Verify available disk space\n")
+	}
+}
+
+// Helper methods for specific suggestions
+func (ef *ErrorFormatter) suggestFileAccess(filePath string) {
+	ef.ui.printf("  • Check if the path exists: %s\n", filePath)
+	ef.ui.printf("  • Verify read permissions\n")
+	if filePath != "" {
+		if stat, err := os.Stat(filePath); err == nil {
+			ef.ui.printf("  • Path exists but may not be accessible\n")
+			ef.ui.printf("  • Mode: %s\n", stat.Mode())
+		}
+	}
+}
+
+func (ef *ErrorFormatter) suggestPathResolution(filePath string) {
+	ef.ui.printf("  • Use an absolute path instead of relative\n")
+	if filePath != "" {
+		if abs, err := filepath.Abs(filePath); err == nil {
+			ef.ui.printf("  • Try: %s\n", abs)
+		}
+	}
+}
+
+func (ef *ErrorFormatter) suggestFileNotFound(filePath string) {
+	ef.ui.printf("  • Check if the file/directory exists: %s\n", filePath)
+	if filePath != "" {
+		dir := filepath.Dir(filePath)
+		if entries, err := os.ReadDir(dir); err == nil {
+			ef.ui.printf("  • Similar files in %s:\n", dir)
+			count := 0
+			for _, entry := range entries {
+				if count >= 3 {
+					break
+				}
+				if strings.Contains(entry.Name(), filepath.Base(filePath)) {
+					ef.ui.printf("    - %s\n", entry.Name())
+					count++
+				}
+			}
+		}
+	}
+}
+
+func (ef *ErrorFormatter) suggestFileSystemGeneral(filePath string) {
+	ef.ui.printf("  • Check file/directory permissions\n")
+	ef.ui.printf("  • Verify the path is correct\n")
+	if filePath != "" {
+		ef.ui.printf("  • Path: %s\n", filePath)
+	}
+}
+
+// provideDefaultSuggestions provides general suggestions.
+func (ef *ErrorFormatter) provideDefaultSuggestions() {
+	ef.ui.printf("  • Check your command line arguments\n")
+	ef.ui.printf("  • Run with --help for usage information\n")
+	ef.ui.printf("  • Try with -concurrency 1 to reduce resource usage\n")
+}
+
+// provideGenericSuggestions provides suggestions for generic errors.
+func (ef *ErrorFormatter) provideGenericSuggestions(err error) {
+	errorMsg := err.Error()
+
+	ef.ui.PrintWarning("Suggestions:")
+
+	// Pattern matching for common errors
+	switch {
+	case strings.Contains(errorMsg, "permission denied"):
+		ef.ui.printf("  • Check file/directory permissions\n")
+		ef.ui.printf("  • Try running with appropriate privileges\n")
+	case strings.Contains(errorMsg, "no such file or directory"):
+		ef.ui.printf("  • Verify the file/directory path is correct\n")
+		ef.ui.printf("  • Check if the file exists\n")
+	case strings.Contains(errorMsg, "flag") && strings.Contains(errorMsg, "redefined"):
+		ef.ui.printf("  • This is likely a test environment issue\n")
+		ef.ui.printf("  • Try running the command directly instead of in tests\n")
+	default:
+		ef.provideDefaultSuggestions()
+	}
+}
+
+// CLI-specific error types
+
+// CLIMissingSourceError represents a missing source directory error.
+type CLIMissingSourceError struct{}
+
+func (e CLIMissingSourceError) Error() string {
+	return "source directory is required"
+}
+
+// NewCLIMissingSourceError creates a new CLI missing source error with suggestions.
+func NewCLIMissingSourceError() error {
+	return &CLIMissingSourceError{}
+}
+
+// IsUserError checks if an error is a user input error that should be handled gracefully.
+func IsUserError(err error) bool {
+	if err == nil {
+		return false
+	}
+
+	// Check for specific user error types
+	var cliErr *CLIMissingSourceError
+	if errors.As(err, &cliErr) {
+		return true
+	}
+
+	// Check for structured errors that are user-facing
+	if structErr, ok := err.(*utils.StructuredError); ok {
+		return structErr.Type == utils.ErrorTypeValidation ||
+			structErr.Code == utils.CodeValidationFormat ||
+			structErr.Code == utils.CodeValidationSize
+	}
+
+	// Check error message patterns
+	errMsg := err.Error()
+	userErrorPatterns := []string{
+		"flag",
+		"usage",
+		"invalid argument",
+		"file not found",
+		"permission denied",
+	}
+
+	for _, pattern := range userErrorPatterns {
+		if strings.Contains(strings.ToLower(errMsg), pattern) {
+			return true
+		}
+	}
+
+	return false
+}
diff --git a/cli/flags.go b/cli/flags.go
new file mode 100644
index 0000000..d18ab3e
--- /dev/null
+++ b/cli/flags.go
@@ -0,0 +1,93 @@
+package cli
+
+import (
+	"flag"
+	"runtime"
+
+	"github.com/ivuorinen/gibidify/config"
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+// Flags holds CLI flags values.
+type Flags struct {
+	SourceDir   string
+	Destination string
+	Prefix      string
+	Suffix      string
+	Concurrency int
+	Format      string
+	NoColors    bool
+	NoProgress  bool
+	Verbose     bool
+}
+
+var (
+	flagsParsed bool
+	globalFlags *Flags
+)
+
+// ParseFlags parses and validates CLI flags.
+func ParseFlags() (*Flags, error) {
+	if flagsParsed {
+		return globalFlags, nil
+	}
+
+	flags := &Flags{}
+
+	flag.StringVar(&flags.SourceDir, "source", "", "Source directory to scan recursively")
+	flag.StringVar(&flags.Destination, "destination", "", "Output file to write aggregated code")
+	flag.StringVar(&flags.Prefix, "prefix", "", "Text to add at the beginning of the output file")
+	flag.StringVar(&flags.Suffix, "suffix", "", "Text to add at the end of the output file")
+	flag.StringVar(&flags.Format, "format", "markdown", "Output format (json, markdown, yaml)")
+	flag.IntVar(&flags.Concurrency, "concurrency", runtime.NumCPU(),
+		"Number of concurrent workers (default: number of CPU cores)")
+	flag.BoolVar(&flags.NoColors, "no-colors", false, "Disable colored output")
+	flag.BoolVar(&flags.NoProgress, "no-progress", false, "Disable progress bars")
+	flag.BoolVar(&flags.Verbose, "verbose", false, "Enable verbose output")
+
+	flag.Parse()
+
+	if err := flags.validate(); err != nil {
+		return nil, err
+	}
+
+	if err := flags.setDefaultDestination(); err != nil {
+		return nil, err
+	}
+
+	flagsParsed = true
+	globalFlags = flags
+	return flags, nil
+}
+
+// validate validates the CLI flags.
+func (f *Flags) validate() error {
+	if f.SourceDir == "" {
+		return NewCLIMissingSourceError()
+	}
+
+	// Validate output format
+	if err := config.ValidateOutputFormat(f.Format); err != nil {
+		return err
+	}
+
+	// Validate concurrency
+	if err := config.ValidateConcurrency(f.Concurrency); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// setDefaultDestination sets the default destination if not provided.
+func (f *Flags) setDefaultDestination() error {
+	if f.Destination == "" {
+		absRoot, err := utils.GetAbsolutePath(f.SourceDir)
+		if err != nil {
+			return err
+		}
+		baseName := utils.GetBaseName(absRoot)
+		f.Destination = baseName + "." + f.Format
+	}
+	return nil
+}
diff --git a/cli/processor.go b/cli/processor.go
new file mode 100644
index 0000000..5c2cd1d
--- /dev/null
+++ b/cli/processor.go
@@ -0,0 +1,210 @@
+package cli
+
+import (
+	"context"
+	"os"
+	"sync"
+
+	"github.com/sirupsen/logrus"
+
+	"github.com/ivuorinen/gibidify/config"
+	"github.com/ivuorinen/gibidify/fileproc"
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+// Processor handles the main file processing logic.
+type Processor struct {
+	flags        *Flags
+	backpressure *fileproc.BackpressureManager
+	ui           *UIManager
+}
+
+// NewProcessor creates a new processor with the given flags.
+func NewProcessor(flags *Flags) *Processor {
+	ui := NewUIManager()
+
+	// Configure UI based on flags
+	ui.SetColorOutput(!flags.NoColors)
+	ui.SetProgressOutput(!flags.NoProgress)
+
+	return &Processor{
+		flags:        flags,
+		backpressure: fileproc.NewBackpressureManager(),
+		ui:           ui,
+	}
+}
+
+// Process executes the main file processing workflow.
+func (p *Processor) Process(ctx context.Context) error {
+	// Configure file type registry
+	p.configureFileTypes()
+
+	// Print startup info with colors
+	p.ui.PrintHeader("🚀 Starting gibidify")
+	p.ui.PrintInfo("Format: %s", p.flags.Format)
+	p.ui.PrintInfo("Source: %s", p.flags.SourceDir)
+	p.ui.PrintInfo("Destination: %s", p.flags.Destination)
+	p.ui.PrintInfo("Workers: %d", p.flags.Concurrency)
+
+	// Collect files with progress indication
+	p.ui.PrintInfo("📁 Collecting files...")
+	files, err := p.collectFiles()
+	if err != nil {
+		return err
+	}
+
+	// Show collection results
+	p.ui.PrintSuccess("Found %d files to process", len(files))
+
+	// Process files
+	return p.processFiles(ctx, files)
+}
+
+// configureFileTypes configures the file type registry.
+func (p *Processor) configureFileTypes() {
+	if config.GetFileTypesEnabled() {
+		fileproc.ConfigureFromSettings(
+			config.GetCustomImageExtensions(),
+			config.GetCustomBinaryExtensions(),
+			config.GetCustomLanguages(),
+			config.GetDisabledImageExtensions(),
+			config.GetDisabledBinaryExtensions(),
+			config.GetDisabledLanguageExtensions(),
+		)
+	}
+}
+
+// collectFiles collects all files to be processed.
+func (p *Processor) collectFiles() ([]string, error) {
+	files, err := fileproc.CollectFiles(p.flags.SourceDir)
+	if err != nil {
+		return nil, utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "error collecting files")
+	}
+	logrus.Infof("Found %d files to process", len(files))
+	return files, nil
+}
+
+// processFiles processes the collected files.
+func (p *Processor) processFiles(ctx context.Context, files []string) error {
+	outFile, err := p.createOutputFile()
+	if err != nil {
+		return err
+	}
+	defer func() {
+		utils.LogError("Error closing output file", outFile.Close())
+	}()
+
+	// Initialize back-pressure and channels
+	p.ui.PrintInfo("⚙️  Initializing processing...")
+	p.backpressure.LogBackpressureInfo()
+	fileCh, writeCh := p.backpressure.CreateChannels()
+	writerDone := make(chan struct{})
+
+	// Start writer
+	go fileproc.StartWriter(outFile, writeCh, writerDone, p.flags.Format, p.flags.Prefix, p.flags.Suffix)
+
+	// Start workers
+	var wg sync.WaitGroup
+	p.startWorkers(ctx, &wg, fileCh, writeCh)
+
+	// Start progress bar
+	p.ui.StartProgress(len(files), "📝 Processing files")
+
+	// Send files to workers
+	if err := p.sendFiles(ctx, files, fileCh); err != nil {
+		p.ui.FinishProgress()
+		return err
+	}
+
+	// Wait for completion
+	p.waitForCompletion(&wg, writeCh, writerDone)
+	p.ui.FinishProgress()
+
+	p.logFinalStats()
+	p.ui.PrintSuccess("Processing completed. Output saved to %s", p.flags.Destination)
+	return nil
+}
+
+// createOutputFile creates the output file.
+func (p *Processor) createOutputFile() (*os.File, error) {
+	outFile, err := os.Create(p.flags.Destination) // #nosec G304 - destination is user-provided CLI arg
+	if err != nil {
+		return nil, utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOFileCreate, "failed to create output file").WithFilePath(p.flags.Destination)
+	}
+	return outFile, nil
+}
+
+// startWorkers starts the worker goroutines.
+func (p *Processor) startWorkers(ctx context.Context, wg *sync.WaitGroup, fileCh chan string, writeCh chan fileproc.WriteRequest) {
+	for range p.flags.Concurrency {
+		wg.Add(1)
+		go p.worker(ctx, wg, fileCh, writeCh)
+	}
+}
+
+// worker is the worker goroutine function.
+func (p *Processor) worker(ctx context.Context, wg *sync.WaitGroup, fileCh chan string, writeCh chan fileproc.WriteRequest) {
+	defer wg.Done()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case filePath, ok := <-fileCh:
+			if !ok {
+				return
+			}
+			p.processFile(filePath, writeCh)
+		}
+	}
+}
+
+// processFile processes a single file.
+func (p *Processor) processFile(filePath string, writeCh chan fileproc.WriteRequest) {
+	absRoot, err := utils.GetAbsolutePath(p.flags.SourceDir)
+	if err != nil {
+		utils.LogError("Failed to get absolute path", err)
+		return
+	}
+	fileproc.ProcessFile(filePath, writeCh, absRoot)
+
+	// Update progress bar
+	p.ui.UpdateProgress(1)
+}
+
+// sendFiles sends files to the worker channels with back-pressure handling.
+func (p *Processor) sendFiles(ctx context.Context, files []string, fileCh chan string) error {
+	defer close(fileCh)
+
+	for _, fp := range files {
+		// Check if we should apply back-pressure
+		if p.backpressure.ShouldApplyBackpressure(ctx) {
+			p.backpressure.ApplyBackpressure(ctx)
+		}
+
+		// Wait for channel space if needed
+		p.backpressure.WaitForChannelSpace(ctx, fileCh, nil)
+
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case fileCh <- fp:
+		}
+	}
+	return nil
+}
+
+// waitForCompletion waits for all workers to complete.
+func (p *Processor) waitForCompletion(wg *sync.WaitGroup, writeCh chan fileproc.WriteRequest, writerDone chan struct{}) {
+	wg.Wait()
+	close(writeCh)
+	<-writerDone
+}
+
+// logFinalStats logs the final back-pressure statistics.
+func (p *Processor) logFinalStats() {
+	stats := p.backpressure.GetStats()
+	if stats.Enabled {
+		logrus.Infof("Back-pressure stats: processed=%d files, memory=%dMB/%dMB",
+			stats.FilesProcessed, stats.CurrentMemoryUsage/1024/1024, stats.MaxMemoryUsage/1024/1024)
+	}
+}
diff --git a/cli/ui.go b/cli/ui.go
new file mode 100644
index 0000000..1c7bc27
--- /dev/null
+++ b/cli/ui.go
@@ -0,0 +1,173 @@
+package cli
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"time"
+
+	"github.com/fatih/color"
+	"github.com/schollz/progressbar/v3"
+)
+
+// UIManager handles CLI user interface elements.
+type UIManager struct {
+	enableColors   bool
+	enableProgress bool
+	progressBar    *progressbar.ProgressBar
+	output         io.Writer
+}
+
+// NewUIManager creates a new UI manager.
+func NewUIManager() *UIManager {
+	return &UIManager{
+		enableColors:   isColorTerminal(),
+		enableProgress: isInteractiveTerminal(),
+		output:         os.Stderr, // Progress and colors go to stderr
+	}
+}
+
+// SetColorOutput enables or disables colored output.
+func (ui *UIManager) SetColorOutput(enabled bool) {
+	ui.enableColors = enabled
+	color.NoColor = !enabled
+}
+
+// SetProgressOutput enables or disables progress bars.
+func (ui *UIManager) SetProgressOutput(enabled bool) {
+	ui.enableProgress = enabled
+}
+
+// StartProgress initializes a progress bar for file processing.
+func (ui *UIManager) StartProgress(total int, description string) {
+	if !ui.enableProgress || total <= 0 {
+		return
+	}
+
+	ui.progressBar = progressbar.NewOptions(total,
+		progressbar.OptionSetWriter(ui.output),
+		progressbar.OptionSetDescription(description),
+		progressbar.OptionSetTheme(progressbar.Theme{
+			Saucer:        color.GreenString("█"),
+			SaucerHead:    color.GreenString("█"),
+			SaucerPadding: " ",
+			BarStart:      "[",
+			BarEnd:        "]",
+		}),
+		progressbar.OptionShowCount(),
+		progressbar.OptionShowIts(),
+		progressbar.OptionSetWidth(40),
+		progressbar.OptionThrottle(100*time.Millisecond),
+		progressbar.OptionOnCompletion(func() {
+			_, _ = fmt.Fprint(ui.output, "\n")
+		}),
+		progressbar.OptionSetRenderBlankState(true),
+	)
+}
+
+// UpdateProgress increments the progress bar.
+func (ui *UIManager) UpdateProgress(increment int) {
+	if ui.progressBar != nil {
+		_ = ui.progressBar.Add(increment)
+	}
+}
+
+// FinishProgress completes the progress bar.
+func (ui *UIManager) FinishProgress() {
+	if ui.progressBar != nil {
+		_ = ui.progressBar.Finish()
+		ui.progressBar = nil
+	}
+}
+
+// PrintSuccess prints a success message in green.
+func (ui *UIManager) PrintSuccess(format string, args ...interface{}) {
+	if ui.enableColors {
+		color.Green("✓ "+format, args...)
+	} else {
+		ui.printf("✓ "+format+"\n", args...)
+	}
+}
+
+// PrintError prints an error message in red.
+func (ui *UIManager) PrintError(format string, args ...interface{}) {
+	if ui.enableColors {
+		color.Red("✗ "+format, args...)
+	} else {
+		ui.printf("✗ "+format+"\n", args...)
+	}
+}
+
+// PrintWarning prints a warning message in yellow.
+func (ui *UIManager) PrintWarning(format string, args ...interface{}) {
+	if ui.enableColors {
+		color.Yellow("⚠ "+format, args...)
+	} else {
+		ui.printf("⚠ "+format+"\n", args...)
+	}
+}
+
+// PrintInfo prints an info message in blue.
+func (ui *UIManager) PrintInfo(format string, args ...interface{}) {
+	if ui.enableColors {
+		color.Blue("ℹ "+format, args...)
+	} else {
+		ui.printf("ℹ "+format+"\n", args...)
+	}
+}
+
+// PrintHeader prints a header message in bold.
+func (ui *UIManager) PrintHeader(format string, args ...interface{}) {
+	if ui.enableColors {
+		_, _ = color.New(color.Bold).Fprintf(ui.output, format+"\n", args...)
+	} else {
+		ui.printf(format+"\n", args...)
+	}
+}
+
+// isColorTerminal checks if the terminal supports colors.
+func isColorTerminal() bool {
+	// Check common environment variables
+	term := os.Getenv("TERM")
+	if term == "" || term == "dumb" {
+		return false
+	}
+
+	// Check for CI environments that typically don't support colors
+	if os.Getenv("CI") != "" {
+		// GitHub Actions supports colors
+		if os.Getenv("GITHUB_ACTIONS") == "true" {
+			return true
+		}
+		// Most other CI systems don't
+		return false
+	}
+
+	// Check if NO_COLOR is set (https://no-color.org/)
+	if os.Getenv("NO_COLOR") != "" {
+		return false
+	}
+
+	// Check if FORCE_COLOR is set
+	if os.Getenv("FORCE_COLOR") != "" {
+		return true
+	}
+
+	// Default to true for interactive terminals
+	return isInteractiveTerminal()
+}
+
+// isInteractiveTerminal checks if we're running in an interactive terminal.
+func isInteractiveTerminal() bool {
+	// Check if stderr is a terminal (where we output progress/colors)
+	fileInfo, err := os.Stderr.Stat()
+	if err != nil {
+		return false
+	}
+	return (fileInfo.Mode() & os.ModeCharDevice) != 0
+}
+
+// printf is a helper that ignores printf errors (for UI output).
+func (ui *UIManager) printf(format string, args ...interface{}) {
+	_, _ = fmt.Fprintf(ui.output, format, args...)
+}
diff --git a/cmd/benchmark/main.go b/cmd/benchmark/main.go
new file mode 100644
index 0000000..e5be0ea
--- /dev/null
+++ b/cmd/benchmark/main.go
@@ -0,0 +1,145 @@
+// Package main provides a CLI for running gibidify benchmarks.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"runtime"
+	"strings"
+
+	"github.com/ivuorinen/gibidify/benchmark"
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+var (
+	sourceDir       = flag.String("source", "", "Source directory to benchmark (uses temp files if empty)")
+	benchmarkType   = flag.String("type", "all", "Benchmark type: all, collection, processing, concurrency, format")
+	format          = flag.String("format", "json", "Output format for processing benchmarks")
+	concurrency     = flag.Int("concurrency", runtime.NumCPU(), "Concurrency level for processing benchmarks")
+	concurrencyList = flag.String("concurrency-list", "1,2,4,8", "Comma-separated list of concurrency levels")
+	formatList      = flag.String("format-list", "json,yaml,markdown", "Comma-separated list of formats")
+	numFiles        = flag.Int("files", 100, "Number of files to create for benchmarks")
+)
+
+func main() {
+	flag.Parse()
+
+	if err := runBenchmarks(); err != nil {
+		fmt.Fprintf(os.Stderr, "Benchmark failed: %v\n", err)
+		os.Exit(1)
+	}
+}
+
+func runBenchmarks() error {
+	fmt.Printf("Running gibidify benchmarks...\n")
+	fmt.Printf("Source: %s\n", getSourceDescription())
+	fmt.Printf("Type: %s\n", *benchmarkType)
+	fmt.Printf("CPU cores: %d\n", runtime.NumCPU())
+	fmt.Println()
+
+	switch *benchmarkType {
+	case "all":
+		return benchmark.RunAllBenchmarks(*sourceDir)
+	case "collection":
+		return runCollectionBenchmark()
+	case "processing":
+		return runProcessingBenchmark()
+	case "concurrency":
+		return runConcurrencyBenchmark()
+	case "format":
+		return runFormatBenchmark()
+	default:
+		return utils.NewValidationError(utils.CodeValidationFormat, "invalid benchmark type: "+*benchmarkType)
+	}
+}
+
+func runCollectionBenchmark() error {
+	fmt.Println("Running file collection benchmark...")
+	result, err := benchmark.FileCollectionBenchmark(*sourceDir, *numFiles)
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "file collection benchmark failed")
+	}
+	benchmark.PrintBenchmarkResult(result)
+	return nil
+}
+
+func runProcessingBenchmark() error {
+	fmt.Printf("Running file processing benchmark (format: %s, concurrency: %d)...\n", *format, *concurrency)
+	result, err := benchmark.FileProcessingBenchmark(*sourceDir, *format, *concurrency)
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "file processing benchmark failed")
+	}
+	benchmark.PrintBenchmarkResult(result)
+	return nil
+}
+
+func runConcurrencyBenchmark() error {
+	concurrencyLevels, err := parseConcurrencyList(*concurrencyList)
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeValidation, utils.CodeValidationFormat, "invalid concurrency list")
+	}
+
+	fmt.Printf("Running concurrency benchmark (format: %s, levels: %v)...\n", *format, concurrencyLevels)
+	suite, err := benchmark.ConcurrencyBenchmark(*sourceDir, *format, concurrencyLevels)
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "concurrency benchmark failed")
+	}
+	benchmark.PrintBenchmarkSuite(suite)
+	return nil
+}
+
+func runFormatBenchmark() error {
+	formats := parseFormatList(*formatList)
+	fmt.Printf("Running format benchmark (formats: %v)...\n", formats)
+	suite, err := benchmark.FormatBenchmark(*sourceDir, formats)
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingCollection, "format benchmark failed")
+	}
+	benchmark.PrintBenchmarkSuite(suite)
+	return nil
+}
+
+func getSourceDescription() string {
+	if *sourceDir == "" {
+		return fmt.Sprintf("temporary files (%d files)", *numFiles)
+	}
+	return *sourceDir
+}
+
+func parseConcurrencyList(list string) ([]int, error) {
+	parts := strings.Split(list, ",")
+	levels := make([]int, 0, len(parts))
+
+	for _, part := range parts {
+		part = strings.TrimSpace(part)
+		var level int
+		if _, err := fmt.Sscanf(part, "%d", &level); err != nil {
+			return nil, utils.WrapErrorf(err, utils.ErrorTypeValidation, utils.CodeValidationFormat, "invalid concurrency level: %s", part)
+		}
+		if level <= 0 {
+			return nil, utils.NewValidationError(utils.CodeValidationFormat, "concurrency level must be positive: "+part)
+		}
+		levels = append(levels, level)
+	}
+
+	if len(levels) == 0 {
+		return nil, utils.NewValidationError(utils.CodeValidationFormat, "no valid concurrency levels found")
+	}
+
+	return levels, nil
+}
+
+func parseFormatList(list string) []string {
+	parts := strings.Split(list, ",")
+	formats := make([]string, 0, len(parts))
+
+	for _, part := range parts {
+		part = strings.TrimSpace(part)
+		if part != "" {
+			formats = append(formats, part)
+		}
+	}
+
+	return formats
+}
diff --git a/config.example.yaml b/config.example.yaml
new file mode 100644
index 0000000..fad9a43
--- /dev/null
+++ b/config.example.yaml
@@ -0,0 +1,84 @@
+# gibidify configuration example
+# Place this file in one of these locations:
+# - $XDG_CONFIG_HOME/gibidify/config.yaml
+# - $HOME/.config/gibidify/config.yaml
+# - Current directory (if no gibidify.yaml output file exists)
+
+# File size limit in bytes (default: 5MB)
+fileSizeLimit: 5242880
+
+# Directories to ignore during scanning
+ignoreDirectories:
+  - vendor
+  - node_modules
+  - .git
+  - dist
+  - build
+  - target
+  - bower_components
+  - cache
+  - tmp
+  - .next
+  - .nuxt
+
+# FileType registry configuration
+fileTypes:
+  # Enable/disable file type detection entirely (default: true)
+  enabled: true
+  
+  # Add custom image extensions
+  customImageExtensions:
+    - .webp
+    - .avif
+    - .heic
+    - .jxl
+  
+  # Add custom binary extensions
+  customBinaryExtensions:
+    - .custom
+    - .proprietary
+    - .blob
+  
+  # Add custom language mappings
+  customLanguages:
+    .zig: zig
+    .odin: odin
+    .v: vlang
+    .grain: grain
+    .gleam: gleam
+    .roc: roc
+    .janet: janet
+    .fennel: fennel
+    .wast: wast
+    .wat: wat
+  
+  # Disable specific default image extensions
+  disabledImageExtensions:
+    - .bmp  # Disable bitmap support
+    - .tif  # Disable TIFF support
+  
+  # Disable specific default binary extensions
+  disabledBinaryExtensions:
+    - .exe  # Don't treat executables as binary
+    - .dll  # Don't treat DLL files as binary
+  
+  # Disable specific default language extensions
+  disabledLanguageExtensions:
+    - .bat  # Don't detect batch files
+    - .cmd  # Don't detect command files
+
+# Maximum concurrency (optional)
+maxConcurrency: 16
+
+# Supported output formats (optional validation)
+supportedFormats:
+  - json
+  - yaml
+  - markdown
+
+# File patterns for filtering (optional)
+filePatterns:
+  - "*.go"
+  - "*.py"
+  - "*.js"
+  - "*.ts"
\ No newline at end of file
diff --git a/config/config.go b/config/config.go
index 13ec049..5e7fd80 100644
--- a/config/config.go
+++ b/config/config.go
@@ -2,11 +2,24 @@
 package config
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/viper"
+
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+const (
+	// DefaultFileSizeLimit is the default maximum file size (5MB).
+	DefaultFileSizeLimit = 5242880
+	// MinFileSizeLimit is the minimum allowed file size limit (1KB).
+	MinFileSizeLimit = 1024
+	// MaxFileSizeLimit is the maximum allowed file size limit (100MB).
+	MaxFileSizeLimit = 104857600
 )
 
 // LoadConfig reads configuration from a YAML file.
@@ -23,23 +36,51 @@ func LoadConfig() {
 	} else if home, err := os.UserHomeDir(); err == nil {
 		viper.AddConfigPath(filepath.Join(home, ".config", "gibidify"))
 	}
-	viper.AddConfigPath(".")
+	// Only add current directory if no config file named gibidify.yaml exists
+	// to avoid conflicts with the project's output file
+	if _, err := os.Stat("gibidify.yaml"); os.IsNotExist(err) {
+		viper.AddConfigPath(".")
+	}
 
 	if err := viper.ReadInConfig(); err != nil {
 		logrus.Infof("Config file not found, using default values: %v", err)
 		setDefaultConfig()
 	} else {
 		logrus.Infof("Using config file: %s", viper.ConfigFileUsed())
+		// Validate configuration after loading
+		if err := ValidateConfig(); err != nil {
+			logrus.Warnf("Configuration validation failed: %v", err)
+			logrus.Info("Falling back to default configuration")
+			// Reset viper and set defaults when validation fails
+			viper.Reset()
+			setDefaultConfig()
+		}
 	}
 }
 
 // setDefaultConfig sets default configuration values.
 func setDefaultConfig() {
-	viper.SetDefault("fileSizeLimit", 5242880) // 5 MB
+	viper.SetDefault("fileSizeLimit", DefaultFileSizeLimit)
 	// Default ignored directories.
 	viper.SetDefault("ignoreDirectories", []string{
 		"vendor", "node_modules", ".git", "dist", "build", "target", "bower_components", "cache", "tmp",
 	})
+
+	// FileTypeRegistry defaults
+	viper.SetDefault("fileTypes.enabled", true)
+	viper.SetDefault("fileTypes.customImageExtensions", []string{})
+	viper.SetDefault("fileTypes.customBinaryExtensions", []string{})
+	viper.SetDefault("fileTypes.customLanguages", map[string]string{})
+	viper.SetDefault("fileTypes.disabledImageExtensions", []string{})
+	viper.SetDefault("fileTypes.disabledBinaryExtensions", []string{})
+	viper.SetDefault("fileTypes.disabledLanguageExtensions", []string{})
+
+	// Back-pressure and memory management defaults
+	viper.SetDefault("backpressure.enabled", true)
+	viper.SetDefault("backpressure.maxPendingFiles", 1000)     // Max files in file channel buffer
+	viper.SetDefault("backpressure.maxPendingWrites", 100)     // Max writes in write channel buffer
+	viper.SetDefault("backpressure.maxMemoryUsage", 104857600) // 100MB max memory usage
+	viper.SetDefault("backpressure.memoryCheckInterval", 1000) // Check memory every 1000 files
 }
 
 // GetFileSizeLimit returns the file size limit from configuration.
@@ -51,3 +92,303 @@ func GetFileSizeLimit() int64 {
 func GetIgnoredDirectories() []string {
 	return viper.GetStringSlice("ignoreDirectories")
 }
+
+// ValidateConfig validates the loaded configuration.
+func ValidateConfig() error {
+	var validationErrors []string
+
+	// Validate file size limit
+	fileSizeLimit := viper.GetInt64("fileSizeLimit")
+	if fileSizeLimit < MinFileSizeLimit {
+		validationErrors = append(validationErrors, fmt.Sprintf("fileSizeLimit (%d) is below minimum (%d)", fileSizeLimit, MinFileSizeLimit))
+	}
+	if fileSizeLimit > MaxFileSizeLimit {
+		validationErrors = append(validationErrors, fmt.Sprintf("fileSizeLimit (%d) exceeds maximum (%d)", fileSizeLimit, MaxFileSizeLimit))
+	}
+
+	// Validate ignore directories
+	ignoreDirectories := viper.GetStringSlice("ignoreDirectories")
+	for i, dir := range ignoreDirectories {
+		dir = strings.TrimSpace(dir)
+		if dir == "" {
+			validationErrors = append(validationErrors, fmt.Sprintf("ignoreDirectories[%d] is empty", i))
+			continue
+		}
+		if strings.Contains(dir, "/") {
+			validationErrors = append(validationErrors, fmt.Sprintf("ignoreDirectories[%d] (%s) contains path separator - only directory names are allowed", i, dir))
+		}
+		if strings.HasPrefix(dir, ".") && dir != ".git" && dir != ".vscode" && dir != ".idea" {
+			validationErrors = append(validationErrors, fmt.Sprintf("ignoreDirectories[%d] (%s) starts with dot - this may cause unexpected behavior", i, dir))
+		}
+	}
+
+	// Validate supported output formats if configured
+	if viper.IsSet("supportedFormats") {
+		supportedFormats := viper.GetStringSlice("supportedFormats")
+		validFormats := map[string]bool{"json": true, "yaml": true, "markdown": true}
+		for i, format := range supportedFormats {
+			format = strings.ToLower(strings.TrimSpace(format))
+			if !validFormats[format] {
+				validationErrors = append(validationErrors, fmt.Sprintf("supportedFormats[%d] (%s) is not a valid format (json, yaml, markdown)", i, format))
+			}
+		}
+	}
+
+	// Validate concurrency settings if configured
+	if viper.IsSet("maxConcurrency") {
+		maxConcurrency := viper.GetInt("maxConcurrency")
+		if maxConcurrency < 1 {
+			validationErrors = append(validationErrors, fmt.Sprintf("maxConcurrency (%d) must be at least 1", maxConcurrency))
+		}
+		if maxConcurrency > 100 {
+			validationErrors = append(validationErrors, fmt.Sprintf("maxConcurrency (%d) is unreasonably high (max 100)", maxConcurrency))
+		}
+	}
+
+	// Validate file patterns if configured
+	if viper.IsSet("filePatterns") {
+		filePatterns := viper.GetStringSlice("filePatterns")
+		for i, pattern := range filePatterns {
+			pattern = strings.TrimSpace(pattern)
+			if pattern == "" {
+				validationErrors = append(validationErrors, fmt.Sprintf("filePatterns[%d] is empty", i))
+				continue
+			}
+			// Basic validation - patterns should contain at least one alphanumeric character
+			if !strings.ContainsAny(pattern, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789") {
+				validationErrors = append(validationErrors, fmt.Sprintf("filePatterns[%d] (%s) appears to be invalid", i, pattern))
+			}
+		}
+	}
+
+	// Validate FileTypeRegistry configuration
+	if viper.IsSet("fileTypes.customImageExtensions") {
+		customImages := viper.GetStringSlice("fileTypes.customImageExtensions")
+		for i, ext := range customImages {
+			ext = strings.TrimSpace(ext)
+			if ext == "" {
+				validationErrors = append(validationErrors, fmt.Sprintf("fileTypes.customImageExtensions[%d] is empty", i))
+				continue
+			}
+			if !strings.HasPrefix(ext, ".") {
+				validationErrors = append(validationErrors, fmt.Sprintf("fileTypes.customImageExtensions[%d] (%s) must start with a dot", i, ext))
+			}
+		}
+	}
+
+	if viper.IsSet("fileTypes.customBinaryExtensions") {
+		customBinary := viper.GetStringSlice("fileTypes.customBinaryExtensions")
+		for i, ext := range customBinary {
+			ext = strings.TrimSpace(ext)
+			if ext == "" {
+				validationErrors = append(validationErrors, fmt.Sprintf("fileTypes.customBinaryExtensions[%d] is empty", i))
+				continue
+			}
+			if !strings.HasPrefix(ext, ".") {
+				validationErrors = append(validationErrors, fmt.Sprintf("fileTypes.customBinaryExtensions[%d] (%s) must start with a dot", i, ext))
+			}
+		}
+	}
+
+	if viper.IsSet("fileTypes.customLanguages") {
+		customLangs := viper.GetStringMapString("fileTypes.customLanguages")
+		for ext, lang := range customLangs {
+			ext = strings.TrimSpace(ext)
+			lang = strings.TrimSpace(lang)
+			if ext == "" {
+				validationErrors = append(validationErrors, "fileTypes.customLanguages contains empty extension key")
+				continue
+			}
+			if !strings.HasPrefix(ext, ".") {
+				validationErrors = append(validationErrors, fmt.Sprintf("fileTypes.customLanguages extension (%s) must start with a dot", ext))
+			}
+			if lang == "" {
+				validationErrors = append(validationErrors, fmt.Sprintf("fileTypes.customLanguages[%s] has empty language value", ext))
+			}
+		}
+	}
+
+	// Validate back-pressure configuration
+	if viper.IsSet("backpressure.maxPendingFiles") {
+		maxPendingFiles := viper.GetInt("backpressure.maxPendingFiles")
+		if maxPendingFiles < 1 {
+			validationErrors = append(validationErrors, fmt.Sprintf("backpressure.maxPendingFiles (%d) must be at least 1", maxPendingFiles))
+		}
+		if maxPendingFiles > 100000 {
+			validationErrors = append(validationErrors, fmt.Sprintf("backpressure.maxPendingFiles (%d) is unreasonably high (max 100000)", maxPendingFiles))
+		}
+	}
+
+	if viper.IsSet("backpressure.maxPendingWrites") {
+		maxPendingWrites := viper.GetInt("backpressure.maxPendingWrites")
+		if maxPendingWrites < 1 {
+			validationErrors = append(validationErrors, fmt.Sprintf("backpressure.maxPendingWrites (%d) must be at least 1", maxPendingWrites))
+		}
+		if maxPendingWrites > 10000 {
+			validationErrors = append(validationErrors, fmt.Sprintf("backpressure.maxPendingWrites (%d) is unreasonably high (max 10000)", maxPendingWrites))
+		}
+	}
+
+	if viper.IsSet("backpressure.maxMemoryUsage") {
+		maxMemoryUsage := viper.GetInt64("backpressure.maxMemoryUsage")
+		if maxMemoryUsage < 1048576 { // 1MB minimum
+			validationErrors = append(validationErrors, fmt.Sprintf("backpressure.maxMemoryUsage (%d) must be at least 1MB (1048576 bytes)", maxMemoryUsage))
+		}
+		if maxMemoryUsage > 10737418240 { // 10GB maximum
+			validationErrors = append(validationErrors, fmt.Sprintf("backpressure.maxMemoryUsage (%d) is unreasonably high (max 10GB)", maxMemoryUsage))
+		}
+	}
+
+	if viper.IsSet("backpressure.memoryCheckInterval") {
+		interval := viper.GetInt("backpressure.memoryCheckInterval")
+		if interval < 1 {
+			validationErrors = append(validationErrors, fmt.Sprintf("backpressure.memoryCheckInterval (%d) must be at least 1", interval))
+		}
+		if interval > 100000 {
+			validationErrors = append(validationErrors, fmt.Sprintf("backpressure.memoryCheckInterval (%d) is unreasonably high (max 100000)", interval))
+		}
+	}
+
+	if len(validationErrors) > 0 {
+		return utils.NewStructuredError(
+			utils.ErrorTypeConfiguration,
+			utils.CodeConfigValidation,
+			"configuration validation failed: "+strings.Join(validationErrors, "; "),
+		).WithContext("validation_errors", validationErrors)
+	}
+
+	return nil
+}
+
+// GetMaxConcurrency returns the maximum concurrency limit from configuration.
+func GetMaxConcurrency() int {
+	return viper.GetInt("maxConcurrency")
+}
+
+// GetSupportedFormats returns the supported output formats from configuration.
+func GetSupportedFormats() []string {
+	return viper.GetStringSlice("supportedFormats")
+}
+
+// GetFilePatterns returns the file patterns from configuration.
+func GetFilePatterns() []string {
+	return viper.GetStringSlice("filePatterns")
+}
+
+// IsValidFormat checks if a format is supported.
+func IsValidFormat(format string) bool {
+	format = strings.ToLower(strings.TrimSpace(format))
+	validFormats := map[string]bool{"json": true, "yaml": true, "markdown": true}
+	return validFormats[format]
+}
+
+// ValidateFileSize checks if a file size is within the configured limit.
+func ValidateFileSize(size int64) error {
+	limit := GetFileSizeLimit()
+	if size > limit {
+		return utils.NewStructuredError(
+			utils.ErrorTypeValidation,
+			utils.CodeValidationSize,
+			fmt.Sprintf("file size (%d bytes) exceeds limit (%d bytes)", size, limit),
+		).WithContext("file_size", size).WithContext("size_limit", limit)
+	}
+	return nil
+}
+
+// ValidateOutputFormat checks if an output format is valid.
+func ValidateOutputFormat(format string) error {
+	if !IsValidFormat(format) {
+		return utils.NewStructuredError(
+			utils.ErrorTypeValidation,
+			utils.CodeValidationFormat,
+			fmt.Sprintf("unsupported output format: %s (supported: json, yaml, markdown)", format),
+		).WithContext("format", format)
+	}
+	return nil
+}
+
+// ValidateConcurrency checks if a concurrency level is valid.
+func ValidateConcurrency(concurrency int) error {
+	if concurrency < 1 {
+		return utils.NewStructuredError(
+			utils.ErrorTypeValidation,
+			utils.CodeValidationFormat,
+			fmt.Sprintf("concurrency (%d) must be at least 1", concurrency),
+		).WithContext("concurrency", concurrency)
+	}
+
+	if viper.IsSet("maxConcurrency") {
+		maxConcurrency := GetMaxConcurrency()
+		if concurrency > maxConcurrency {
+			return utils.NewStructuredError(
+				utils.ErrorTypeValidation,
+				utils.CodeValidationFormat,
+				fmt.Sprintf("concurrency (%d) exceeds maximum (%d)", concurrency, maxConcurrency),
+			).WithContext("concurrency", concurrency).WithContext("max_concurrency", maxConcurrency)
+		}
+	}
+
+	return nil
+}
+
+// GetFileTypesEnabled returns whether file type detection is enabled.
+func GetFileTypesEnabled() bool {
+	return viper.GetBool("fileTypes.enabled")
+}
+
+// GetCustomImageExtensions returns custom image extensions from configuration.
+func GetCustomImageExtensions() []string {
+	return viper.GetStringSlice("fileTypes.customImageExtensions")
+}
+
+// GetCustomBinaryExtensions returns custom binary extensions from configuration.
+func GetCustomBinaryExtensions() []string {
+	return viper.GetStringSlice("fileTypes.customBinaryExtensions")
+}
+
+// GetCustomLanguages returns custom language mappings from configuration.
+func GetCustomLanguages() map[string]string {
+	return viper.GetStringMapString("fileTypes.customLanguages")
+}
+
+// GetDisabledImageExtensions returns disabled image extensions from configuration.
+func GetDisabledImageExtensions() []string {
+	return viper.GetStringSlice("fileTypes.disabledImageExtensions")
+}
+
+// GetDisabledBinaryExtensions returns disabled binary extensions from configuration.
+func GetDisabledBinaryExtensions() []string {
+	return viper.GetStringSlice("fileTypes.disabledBinaryExtensions")
+}
+
+// GetDisabledLanguageExtensions returns disabled language extensions from configuration.
+func GetDisabledLanguageExtensions() []string {
+	return viper.GetStringSlice("fileTypes.disabledLanguageExtensions")
+}
+
+// Back-pressure configuration getters
+
+// GetBackpressureEnabled returns whether back-pressure management is enabled.
+func GetBackpressureEnabled() bool {
+	return viper.GetBool("backpressure.enabled")
+}
+
+// GetMaxPendingFiles returns the maximum number of files that can be pending in the file channel.
+func GetMaxPendingFiles() int {
+	return viper.GetInt("backpressure.maxPendingFiles")
+}
+
+// GetMaxPendingWrites returns the maximum number of writes that can be pending in the write channel.
+func GetMaxPendingWrites() int {
+	return viper.GetInt("backpressure.maxPendingWrites")
+}
+
+// GetMaxMemoryUsage returns the maximum memory usage in bytes before back-pressure kicks in.
+func GetMaxMemoryUsage() int64 {
+	return viper.GetInt64("backpressure.maxMemoryUsage")
+}
+
+// GetMemoryCheckInterval returns how often to check memory usage (in number of files processed).
+func GetMemoryCheckInterval() int {
+	return viper.GetInt("backpressure.memoryCheckInterval")
+}
diff --git a/config/config_filetype_test.go b/config/config_filetype_test.go
new file mode 100644
index 0000000..0065bfa
--- /dev/null
+++ b/config/config_filetype_test.go
@@ -0,0 +1,174 @@
+package config
+
+import (
+	"testing"
+
+	"github.com/spf13/viper"
+)
+
+// TestFileTypeRegistryConfig tests the FileTypeRegistry configuration functionality.
+func TestFileTypeRegistryConfig(t *testing.T) {
+	// Test default values
+	t.Run("DefaultValues", func(t *testing.T) {
+		viper.Reset()
+		setDefaultConfig()
+
+		if !GetFileTypesEnabled() {
+			t.Error("Expected file types to be enabled by default")
+		}
+
+		if len(GetCustomImageExtensions()) != 0 {
+			t.Error("Expected custom image extensions to be empty by default")
+		}
+
+		if len(GetCustomBinaryExtensions()) != 0 {
+			t.Error("Expected custom binary extensions to be empty by default")
+		}
+
+		if len(GetCustomLanguages()) != 0 {
+			t.Error("Expected custom languages to be empty by default")
+		}
+
+		if len(GetDisabledImageExtensions()) != 0 {
+			t.Error("Expected disabled image extensions to be empty by default")
+		}
+
+		if len(GetDisabledBinaryExtensions()) != 0 {
+			t.Error("Expected disabled binary extensions to be empty by default")
+		}
+
+		if len(GetDisabledLanguageExtensions()) != 0 {
+			t.Error("Expected disabled language extensions to be empty by default")
+		}
+	})
+
+	// Test configuration setting and getting
+	t.Run("ConfigurationSetGet", func(t *testing.T) {
+		viper.Reset()
+
+		// Set test values
+		viper.Set("fileTypes.enabled", false)
+		viper.Set("fileTypes.customImageExtensions", []string{".webp", ".avif"})
+		viper.Set("fileTypes.customBinaryExtensions", []string{".custom", ".mybin"})
+		viper.Set("fileTypes.customLanguages", map[string]string{
+			".zig": "zig",
+			".v":   "vlang",
+		})
+		viper.Set("fileTypes.disabledImageExtensions", []string{".gif", ".bmp"})
+		viper.Set("fileTypes.disabledBinaryExtensions", []string{".exe", ".dll"})
+		viper.Set("fileTypes.disabledLanguageExtensions", []string{".rb", ".pl"})
+
+		// Test getter functions
+		if GetFileTypesEnabled() {
+			t.Error("Expected file types to be disabled")
+		}
+
+		customImages := GetCustomImageExtensions()
+		expectedImages := []string{".webp", ".avif"}
+		if len(customImages) != len(expectedImages) {
+			t.Errorf("Expected %d custom image extensions, got %d", len(expectedImages), len(customImages))
+		}
+		for i, ext := range expectedImages {
+			if customImages[i] != ext {
+				t.Errorf("Expected custom image extension %s, got %s", ext, customImages[i])
+			}
+		}
+
+		customBinary := GetCustomBinaryExtensions()
+		expectedBinary := []string{".custom", ".mybin"}
+		if len(customBinary) != len(expectedBinary) {
+			t.Errorf("Expected %d custom binary extensions, got %d", len(expectedBinary), len(customBinary))
+		}
+		for i, ext := range expectedBinary {
+			if customBinary[i] != ext {
+				t.Errorf("Expected custom binary extension %s, got %s", ext, customBinary[i])
+			}
+		}
+
+		customLangs := GetCustomLanguages()
+		expectedLangs := map[string]string{
+			".zig": "zig",
+			".v":   "vlang",
+		}
+		if len(customLangs) != len(expectedLangs) {
+			t.Errorf("Expected %d custom languages, got %d", len(expectedLangs), len(customLangs))
+		}
+		for ext, lang := range expectedLangs {
+			if customLangs[ext] != lang {
+				t.Errorf("Expected custom language %s -> %s, got %s", ext, lang, customLangs[ext])
+			}
+		}
+
+		disabledImages := GetDisabledImageExtensions()
+		expectedDisabledImages := []string{".gif", ".bmp"}
+		if len(disabledImages) != len(expectedDisabledImages) {
+			t.Errorf("Expected %d disabled image extensions, got %d", len(expectedDisabledImages), len(disabledImages))
+		}
+
+		disabledBinary := GetDisabledBinaryExtensions()
+		expectedDisabledBinary := []string{".exe", ".dll"}
+		if len(disabledBinary) != len(expectedDisabledBinary) {
+			t.Errorf("Expected %d disabled binary extensions, got %d", len(expectedDisabledBinary), len(disabledBinary))
+		}
+
+		disabledLangs := GetDisabledLanguageExtensions()
+		expectedDisabledLangs := []string{".rb", ".pl"}
+		if len(disabledLangs) != len(expectedDisabledLangs) {
+			t.Errorf("Expected %d disabled language extensions, got %d", len(expectedDisabledLangs), len(disabledLangs))
+		}
+	})
+
+	// Test validation
+	t.Run("ValidationSuccess", func(t *testing.T) {
+		viper.Reset()
+		setDefaultConfig()
+
+		// Set valid configuration
+		viper.Set("fileTypes.customImageExtensions", []string{".webp", ".avif"})
+		viper.Set("fileTypes.customBinaryExtensions", []string{".custom"})
+		viper.Set("fileTypes.customLanguages", map[string]string{
+			".zig": "zig",
+			".v":   "vlang",
+		})
+
+		err := ValidateConfig()
+		if err != nil {
+			t.Errorf("Expected validation to pass with valid config, got error: %v", err)
+		}
+	})
+
+	t.Run("ValidationFailure", func(t *testing.T) {
+		// Test invalid custom image extensions
+		viper.Reset()
+		setDefaultConfig()
+		viper.Set("fileTypes.customImageExtensions", []string{"", "webp"}) // Empty and missing dot
+
+		err := ValidateConfig()
+		if err == nil {
+			t.Error("Expected validation to fail with invalid custom image extensions")
+		}
+
+		// Test invalid custom binary extensions
+		viper.Reset()
+		setDefaultConfig()
+		viper.Set("fileTypes.customBinaryExtensions", []string{"custom"}) // Missing dot
+
+		err = ValidateConfig()
+		if err == nil {
+			t.Error("Expected validation to fail with invalid custom binary extensions")
+		}
+
+		// Test invalid custom languages
+		viper.Reset()
+		setDefaultConfig()
+		viper.Set("fileTypes.customLanguages", map[string]string{
+			"zig": "zig", // Missing dot in extension
+			".v":  "",    // Empty language
+		})
+
+		err = ValidateConfig()
+		if err == nil {
+			t.Error("Expected validation to fail with invalid custom languages")
+		}
+	})
+}
diff --git a/config/config_test.go b/config/config_test.go
index a0b7c8e..55fc55c 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -2,40 +2,38 @@ package config_test
 
 import (
 	"os"
-	"path/filepath"
+	"strings"
 	"testing"
 
-	configpkg "github.com/ivuorinen/gibidify/config"
 	"github.com/spf13/viper"
+
+	"github.com/ivuorinen/gibidify/config"
+	"github.com/ivuorinen/gibidify/testutil"
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+const (
+	defaultFileSizeLimit = 5242880
+	testFileSizeLimit    = 123456
 )
 
 // TestDefaultConfig verifies that if no config file is found,
 // the default configuration values are correctly set.
 func TestDefaultConfig(t *testing.T) {
 	// Create a temporary directory to ensure no config file is present.
-	tmpDir, err := os.MkdirTemp("", "gibidify_config_test_default")
-	if err != nil {
-		t.Fatalf("Failed to create temp directory: %v", err)
-	}
-	defer func() {
-		if err := os.RemoveAll(tmpDir); err != nil {
-			t.Fatalf("cleanup failed: %v", err)
-		}
-	}()
+	tmpDir := t.TempDir()
 
 	// Point Viper to the temp directory with no config file.
 	originalConfigPaths := viper.ConfigFileUsed()
-	viper.Reset()
-	viper.AddConfigPath(tmpDir)
-	configpkg.LoadConfig()
+	testutil.ResetViperConfig(t, tmpDir)
 
 	// Check defaults
-	defaultSizeLimit := configpkg.GetFileSizeLimit()
-	if defaultSizeLimit != 5242880 {
+	defaultSizeLimit := config.GetFileSizeLimit()
+	if defaultSizeLimit != defaultFileSizeLimit {
 		t.Errorf("Expected default file size limit of 5242880, got %d", defaultSizeLimit)
 	}
 
-	ignoredDirs := configpkg.GetIgnoredDirectories()
+	ignoredDirs := config.GetIgnoredDirectories()
 	if len(ignoredDirs) == 0 {
 		t.Errorf("Expected some default ignored directories, got none")
 	}
@@ -47,15 +45,7 @@ func TestDefaultConfig(t *testing.T) {
 // TestLoadConfigFile verifies that when a valid config file is present,
 // viper loads the specified values correctly.
 func TestLoadConfigFile(t *testing.T) {
-	tmpDir, err := os.MkdirTemp("", "gibidify_config_test_file")
-	if err != nil {
-		t.Fatalf("Failed to create temp directory: %v", err)
-	}
-	defer func() {
-		if err := os.RemoveAll(tmpDir); err != nil {
-			t.Fatalf("cleanup failed: %v", err)
-		}
-	}()
+	tmpDir := t.TempDir()
 
 	// Prepare a minimal config file
 	configContent := []byte(`---
@@ -65,22 +55,17 @@ ignoreDirectories:
 - "testdir2"
 `)
 
-	configPath := filepath.Join(tmpDir, "config.yaml")
-	if err := os.WriteFile(configPath, configContent, 0644); err != nil {
-		t.Fatalf("Failed to write config file: %v", err)
-	}
+	testutil.CreateTestFile(t, tmpDir, "config.yaml", configContent)
 
 	// Reset viper and point to the new config path
 	viper.Reset()
 	viper.AddConfigPath(tmpDir)
 
 	// Force Viper to read our config file
-	if err := viper.ReadInConfig(); err != nil {
-		t.Fatalf("Could not read config file: %v", err)
-	}
+	testutil.MustSucceed(t, viper.ReadInConfig(), "reading config file")
 
 	// Validate loaded data
-	if got := viper.GetInt64("fileSizeLimit"); got != 123456 {
+	if got := viper.GetInt64("fileSizeLimit"); got != testFileSizeLimit {
 		t.Errorf("Expected fileSizeLimit=123456, got %d", got)
 	}
 
@@ -89,3 +74,283 @@ ignoreDirectories:
 		t.Errorf("Expected [\"testdir1\", \"testdir2\"], got %v", ignored)
 	}
 }
+
+// TestValidateConfig tests the configuration validation functionality.
+func TestValidateConfig(t *testing.T) {
+	tests := []struct {
+		name        string
+		config      map[string]interface{}
+		wantErr     bool
+		errContains string
+	}{
+		{
+			name: "valid default config",
+			config: map[string]interface{}{
+				"fileSizeLimit":     config.DefaultFileSizeLimit,
+				"ignoreDirectories": []string{"node_modules", ".git"},
+			},
+			wantErr: false,
+		},
+		{
+			name: "file size limit too small",
+			config: map[string]interface{}{
+				"fileSizeLimit": config.MinFileSizeLimit - 1,
+			},
+			wantErr:     true,
+			errContains: "fileSizeLimit",
+		},
+		{
+			name: "file size limit too large",
+			config: map[string]interface{}{
+				"fileSizeLimit": config.MaxFileSizeLimit + 1,
+			},
+			wantErr:     true,
+			errContains: "fileSizeLimit",
+		},
+		{
+			name: "empty ignore directory",
+			config: map[string]interface{}{
+				"ignoreDirectories": []string{"node_modules", "", ".git"},
+			},
+			wantErr:     true,
+			errContains: "ignoreDirectories",
+		},
+		{
+			name: "ignore directory with path separator",
+			config: map[string]interface{}{
+				"ignoreDirectories": []string{"node_modules", "src/build", ".git"},
+			},
+			wantErr:     true,
+			errContains: "path separator",
+		},
+		{
+			name: "invalid supported format",
+			config: map[string]interface{}{
+				"supportedFormats": []string{"json", "xml", "yaml"},
+			},
+			wantErr:     true,
+			errContains: "not a valid format",
+		},
+		{
+			name: "invalid max concurrency",
+			config: map[string]interface{}{
+				"maxConcurrency": 0,
+			},
+			wantErr:     true,
+			errContains: "maxConcurrency",
+		},
+		{
+			name: "valid comprehensive config",
+			config: map[string]interface{}{
+				"fileSizeLimit":     config.DefaultFileSizeLimit,
+				"ignoreDirectories": []string{"node_modules", ".git", ".vscode"},
+				"supportedFormats":  []string{"json", "yaml", "markdown"},
+				"maxConcurrency":    8,
+				"filePatterns":      []string{"*.go", "*.js", "*.py"},
+			},
+			wantErr: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Reset viper for each test
+			viper.Reset()
+
+			// Set test configuration
+			for key, value := range tt.config {
+				viper.Set(key, value)
+			}
+
+			// Load defaults for missing values
+			config.LoadConfig()
+
+			err := config.ValidateConfig()
+
+			if tt.wantErr {
+				if err == nil {
+					t.Errorf("Expected error but got none")
+					return
+				}
+				if tt.errContains != "" && !strings.Contains(err.Error(), tt.errContains) {
+					t.Errorf("Expected error to contain %q, got %q", tt.errContains, err.Error())
+				}
+
+				// Check that it's a structured error
+				var structErr *utils.StructuredError
+				if !errorAs(err, &structErr) {
+					t.Errorf("Expected structured error, got %T", err)
+					return
+				}
+				if structErr.Type != utils.ErrorTypeConfiguration {
+					t.Errorf("Expected error type %v, got %v", utils.ErrorTypeConfiguration, structErr.Type)
+				}
+				if structErr.Code != utils.CodeConfigValidation {
+					t.Errorf("Expected error code %v, got %v", utils.CodeConfigValidation, structErr.Code)
+				}
+			} else {
+				if err != nil {
+					t.Errorf("Expected no error but got: %v", err)
+				}
+			}
+		})
+	}
+}
+
+// TestValidationFunctions tests individual validation functions.
+func TestValidationFunctions(t *testing.T) {
+	t.Run("IsValidFormat", func(t *testing.T) {
+		tests := []struct {
+			format string
+			valid  bool
+		}{
+			{"json", true},
+			{"yaml", true},
+			{"markdown", true},
+			{"JSON", true},
+			{"xml", false},
+			{"txt", false},
+			{"", false},
+			{"  json  ", true},
+		}
+
+		for _, tt := range tests {
+			result := config.IsValidFormat(tt.format)
+			if result != tt.valid {
+				t.Errorf("IsValidFormat(%q) = %v, want %v", tt.format, result, tt.valid)
+			}
+		}
+	})
+
+	t.Run("ValidateFileSize", func(t *testing.T) {
+		viper.Reset()
+		viper.Set("fileSizeLimit", config.DefaultFileSizeLimit)
+
+		tests := []struct {
+			name    string
+			size    int64
+			wantErr bool
+		}{
+			{"size within limit", config.DefaultFileSizeLimit - 1, false},
+			{"size at limit", config.DefaultFileSizeLimit, false},
+			{"size exceeds limit", config.DefaultFileSizeLimit + 1, true},
+			{"zero size", 0, false},
+		}
+
+		for _, tt := range tests {
+			err := config.ValidateFileSize(tt.size)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("%s: ValidateFileSize(%d) error = %v, wantErr %v", tt.name, tt.size, err, tt.wantErr)
+			}
+		}
+	})
+
+	t.Run("ValidateOutputFormat", func(t *testing.T) {
+		tests := []struct {
+			format  string
+			wantErr bool
+		}{
+			{"json", false},
+			{"yaml", false},
+			{"markdown", false},
+			{"xml", true},
+			{"txt", true},
+			{"", true},
+		}
+
+		for _, tt := range tests {
+			err := config.ValidateOutputFormat(tt.format)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ValidateOutputFormat(%q) error = %v, wantErr %v", tt.format, err, tt.wantErr)
+			}
+		}
+	})
+
+	t.Run("ValidateConcurrency", func(t *testing.T) {
+		tests := []struct {
+			name           string
+			concurrency    int
+			maxConcurrency int
+			setMax         bool
+			wantErr        bool
+		}{
+			{"valid concurrency", 4, 0, false, false},
+			{"minimum concurrency", 1, 0, false, false},
+			{"zero concurrency", 0, 0, false, true},
+			{"negative concurrency", -1, 0, false, true},
+			{"concurrency within max", 4, 8, true, false},
+			{"concurrency exceeds max", 16, 8, true, true},
+		}
+
+		for _, tt := range tests {
+			viper.Reset()
+			if tt.setMax {
+				viper.Set("maxConcurrency", tt.maxConcurrency)
+			}
+
+			err := config.ValidateConcurrency(tt.concurrency)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("%s: ValidateConcurrency(%d) error = %v, wantErr %v", tt.name, tt.concurrency, err, tt.wantErr)
+			}
+		}
+	})
+}
+
+// TestLoadConfigWithValidation tests that invalid config files fall back to defaults.
+func TestLoadConfigWithValidation(t *testing.T) {
+	// Create a temporary config file with invalid content
+	configContent := `
+fileSizeLimit: 100
+ignoreDirectories:
+  - node_modules
+  - ""
+  - .git
+`
+
+	tempDir := t.TempDir()
+	configFile := tempDir + "/config.yaml"
+
+	err := os.WriteFile(configFile, []byte(configContent), 0o644)
+	if err != nil {
+		t.Fatalf("Failed to write config file: %v", err)
+	}
+
+	// Reset viper and set config path
+	viper.Reset()
+	viper.AddConfigPath(tempDir)
+
+	// This should load the config but validation should fail and fall back to defaults
+	config.LoadConfig()
+
+	// Should have fallen back to defaults due to validation failure
+	if config.GetFileSizeLimit() != int64(config.DefaultFileSizeLimit) {
+		t.Errorf("Expected default file size limit after validation failure, got %d", config.GetFileSizeLimit())
+	}
+	if containsString(config.GetIgnoredDirectories(), "") {
+		t.Errorf("Expected ignored directories not to contain empty string after validation failure, got %v", config.GetIgnoredDirectories())
+	}
+}
+
+// Helper functions
+
+func containsString(slice []string, item string) bool {
+	for _, s := range slice {
+		if s == item {
+			return true
+		}
+	}
+	return false
+}
+
+func errorAs(err error, target interface{}) bool {
+	if err == nil {
+		return false
+	}
+	if structErr, ok := err.(*utils.StructuredError); ok {
+		if ptr, ok := target.(**utils.StructuredError); ok {
+			*ptr = structErr
+			return true
+		}
+	}
+	return false
+}
diff --git a/fileproc/backpressure.go b/fileproc/backpressure.go
new file mode 100644
index 0000000..733a271
--- /dev/null
+++ b/fileproc/backpressure.go
@@ -0,0 +1,196 @@
+// Package fileproc provides back-pressure management for memory optimization.
+package fileproc
+
+import (
+	"context"
+	"runtime"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/sirupsen/logrus"
+
+	"github.com/ivuorinen/gibidify/config"
+)
+
+// BackpressureManager manages memory usage and applies back-pressure when needed.
+type BackpressureManager struct {
+	enabled             bool
+	maxMemoryUsage      int64
+	memoryCheckInterval int
+	maxPendingFiles     int
+	maxPendingWrites    int
+	filesProcessed      int64
+	mu                  sync.RWMutex
+	memoryWarningLogged bool
+	lastMemoryCheck     time.Time
+}
+
+// NewBackpressureManager creates a new back-pressure manager with configuration.
+func NewBackpressureManager() *BackpressureManager {
+	return &BackpressureManager{
+		enabled:             config.GetBackpressureEnabled(),
+		maxMemoryUsage:      config.GetMaxMemoryUsage(),
+		memoryCheckInterval: config.GetMemoryCheckInterval(),
+		maxPendingFiles:     config.GetMaxPendingFiles(),
+		maxPendingWrites:    config.GetMaxPendingWrites(),
+		lastMemoryCheck:     time.Now(),
+	}
+}
+
+// CreateChannels creates properly sized channels based on back-pressure configuration.
+func (bp *BackpressureManager) CreateChannels() (chan string, chan WriteRequest) {
+	var fileCh chan string
+	var writeCh chan WriteRequest
+
+	if bp.enabled {
+		// Use buffered channels with configured limits
+		fileCh = make(chan string, bp.maxPendingFiles)
+		writeCh = make(chan WriteRequest, bp.maxPendingWrites)
+		logrus.Debugf("Created buffered channels: files=%d, writes=%d", bp.maxPendingFiles, bp.maxPendingWrites)
+	} else {
+		// Use unbuffered channels (default behavior)
+		fileCh = make(chan string)
+		writeCh = make(chan WriteRequest)
+		logrus.Debug("Created unbuffered channels (back-pressure disabled)")
+	}
+
+	return fileCh, writeCh
+}
+
+// ShouldApplyBackpressure checks if back-pressure should be applied.
+func (bp *BackpressureManager) ShouldApplyBackpressure(ctx context.Context) bool {
+	if !bp.enabled {
+		return false
+	}
+
+	// Check if we should evaluate memory usage
+	filesProcessed := atomic.AddInt64(&bp.filesProcessed, 1)
+	if int(filesProcessed)%bp.memoryCheckInterval != 0 {
+		return false
+	}
+
+	// Get current memory usage
+	var m runtime.MemStats
+	runtime.ReadMemStats(&m)
+	currentMemory := int64(m.Alloc)
+
+	bp.mu.Lock()
+	defer bp.mu.Unlock()
+
+	bp.lastMemoryCheck = time.Now()
+
+	// Check if we're over the memory limit
+	if currentMemory > bp.maxMemoryUsage {
+		if !bp.memoryWarningLogged {
+			logrus.Warnf("Memory usage (%d bytes) exceeds limit (%d bytes), applying back-pressure",
+				currentMemory, bp.maxMemoryUsage)
+			bp.memoryWarningLogged = true
+		}
+		return true
+	}
+
+	// Reset warning flag if we're back under the limit
+	if bp.memoryWarningLogged && currentMemory < bp.maxMemoryUsage*8/10 { // 80% of limit
+		logrus.Infof("Memory usage normalized (%d bytes), removing back-pressure", currentMemory)
+		bp.memoryWarningLogged = false
+	}
+
+	return false
+}
+
+// ApplyBackpressure applies back-pressure by triggering garbage collection and adding delay.
+func (bp *BackpressureManager) ApplyBackpressure(ctx context.Context) {
+	if !bp.enabled {
+		return
+	}
+
+	// Force garbage collection to free up memory
+	runtime.GC()
+
+	// Add a small delay to allow memory to be freed
+	select {
+	case <-ctx.Done():
+		return
+	case <-time.After(10 * time.Millisecond):
+		// Small delay to allow GC to complete
+	}
+
+	// Log memory usage after GC
+	var m runtime.MemStats
+	runtime.ReadMemStats(&m)
+	logrus.Debugf("Applied back-pressure: memory after GC = %d bytes", m.Alloc)
+}
+
+// GetStats returns current back-pressure statistics.
+func (bp *BackpressureManager) GetStats() BackpressureStats {
+	bp.mu.RLock()
+	defer bp.mu.RUnlock()
+
+	var m runtime.MemStats
+	runtime.ReadMemStats(&m)
+
+	return BackpressureStats{
+		Enabled:             bp.enabled,
+		FilesProcessed:      atomic.LoadInt64(&bp.filesProcessed),
+		CurrentMemoryUsage:  int64(m.Alloc),
+		MaxMemoryUsage:      bp.maxMemoryUsage,
+		MemoryWarningActive: bp.memoryWarningLogged,
+		LastMemoryCheck:     bp.lastMemoryCheck,
+		MaxPendingFiles:     bp.maxPendingFiles,
+		MaxPendingWrites:    bp.maxPendingWrites,
+	}
+}
+
+// BackpressureStats represents back-pressure manager statistics.
+type BackpressureStats struct {
+	Enabled             bool      `json:"enabled"`
+	FilesProcessed      int64     `json:"files_processed"`
+	CurrentMemoryUsage  int64     `json:"current_memory_usage"`
+	MaxMemoryUsage      int64     `json:"max_memory_usage"`
+	MemoryWarningActive bool      `json:"memory_warning_active"`
+	LastMemoryCheck     time.Time `json:"last_memory_check"`
+	MaxPendingFiles     int       `json:"max_pending_files"`
+	MaxPendingWrites    int       `json:"max_pending_writes"`
+}
+
+// WaitForChannelSpace waits for space in channels if they're getting full.
+func (bp *BackpressureManager) WaitForChannelSpace(ctx context.Context, fileCh chan string, writeCh chan WriteRequest) {
+	if !bp.enabled {
+		return
+	}
+
+	// Check if file channel is getting full (>90% capacity)
+	if len(fileCh) > bp.maxPendingFiles*9/10 {
+		logrus.Debugf("File channel is %d%% full, waiting for space", len(fileCh)*100/bp.maxPendingFiles)
+
+		// Wait a bit for the channel to drain
+		select {
+		case <-ctx.Done():
+			return
+		case <-time.After(5 * time.Millisecond):
+		}
+	}
+
+	// Check if write channel is getting full (>90% capacity)
+	if len(writeCh) > bp.maxPendingWrites*9/10 {
+		logrus.Debugf("Write channel is %d%% full, waiting for space", len(writeCh)*100/bp.maxPendingWrites)
+
+		// Wait a bit for the channel to drain
+		select {
+		case <-ctx.Done():
+			return
+		case <-time.After(5 * time.Millisecond):
+		}
+	}
+}
+
+// LogBackpressureInfo logs back-pressure configuration and status.
+func (bp *BackpressureManager) LogBackpressureInfo() {
+	if bp.enabled {
+		logrus.Infof("Back-pressure enabled: maxMemory=%dMB, fileBuffer=%d, writeBuffer=%d, checkInterval=%d",
+			bp.maxMemoryUsage/1024/1024, bp.maxPendingFiles, bp.maxPendingWrites, bp.memoryCheckInterval)
+	} else {
+		logrus.Info("Back-pressure disabled")
+	}
+}
diff --git a/fileproc/cache.go b/fileproc/cache.go
new file mode 100644
index 0000000..ab3ad60
--- /dev/null
+++ b/fileproc/cache.go
@@ -0,0 +1,127 @@
+package fileproc
+
+// getNormalizedExtension efficiently extracts and normalizes the file extension with caching.
+func (r *FileTypeRegistry) getNormalizedExtension(filename string) string {
+	// Try cache first (read lock)
+	r.cacheMutex.RLock()
+	if ext, exists := r.extCache[filename]; exists {
+		r.cacheMutex.RUnlock()
+		return ext
+	}
+	r.cacheMutex.RUnlock()
+
+	// Compute normalized extension
+	ext := normalizeExtension(filename)
+
+	// Cache the result (write lock)
+	r.cacheMutex.Lock()
+	// Check cache size and clean if needed
+	if len(r.extCache) >= r.maxCacheSize*2 {
+		r.clearExtCache()
+		r.stats.CacheEvictions++
+	}
+	r.extCache[filename] = ext
+	r.cacheMutex.Unlock()
+
+	return ext
+}
+
+// getFileTypeResult gets cached file type detection result or computes it.
+func (r *FileTypeRegistry) getFileTypeResult(filename string) FileTypeResult {
+	ext := r.getNormalizedExtension(filename)
+
+	// Update statistics
+	r.updateStats(func() {
+		r.stats.TotalLookups++
+	})
+
+	// Try cache first (read lock)
+	r.cacheMutex.RLock()
+	if result, exists := r.resultCache[ext]; exists {
+		r.cacheMutex.RUnlock()
+		r.updateStats(func() {
+			r.stats.CacheHits++
+		})
+		return result
+	}
+	r.cacheMutex.RUnlock()
+
+	// Cache miss
+	r.updateStats(func() {
+		r.stats.CacheMisses++
+	})
+
+	// Compute result
+	result := FileTypeResult{
+		Extension: ext,
+		IsImage:   r.imageExts[ext],
+		IsBinary:  r.binaryExts[ext],
+		Language:  r.languageMap[ext],
+	}
+
+	// Handle special cases for binary detection (like .DS_Store)
+	if !result.IsBinary && isSpecialFile(filename, r.binaryExts) {
+		result.IsBinary = true
+	}
+
+	// Cache the result (write lock)
+	r.cacheMutex.Lock()
+	if len(r.resultCache) >= r.maxCacheSize {
+		r.clearResultCache()
+		r.stats.CacheEvictions++
+	}
+	r.resultCache[ext] = result
+	r.cacheMutex.Unlock()
+
+	return result
+}
+
+// clearExtCache clears half of the extension cache (LRU-like behavior).
+func (r *FileTypeRegistry) clearExtCache() {
+	r.clearCache(&r.extCache, r.maxCacheSize)
+}
+
+// clearResultCache clears half of the result cache.
+func (r *FileTypeRegistry) clearResultCache() {
+	newCache := make(map[string]FileTypeResult, r.maxCacheSize)
+	count := 0
+	for k, v := range r.resultCache {
+		if count >= r.maxCacheSize/2 {
+			break
+		}
+		newCache[k] = v
+		count++
+	}
+	r.resultCache = newCache
+}
+
+// clearCache is a generic cache clearing function.
+func (r *FileTypeRegistry) clearCache(cache *map[string]string, maxSize int) {
+	newCache := make(map[string]string, maxSize)
+	count := 0
+	for k, v := range *cache {
+		if count >= maxSize/2 {
+			break
+		}
+		newCache[k] = v
+		count++
+	}
+	*cache = newCache
+}
+
+// invalidateCache clears both caches when the registry is modified.
+func (r *FileTypeRegistry) invalidateCache() {
+	r.cacheMutex.Lock()
+	defer r.cacheMutex.Unlock()
+
+	r.extCache = make(map[string]string, r.maxCacheSize)
+	r.resultCache = make(map[string]FileTypeResult, r.maxCacheSize)
+	r.stats.CacheEvictions++
+}
+
+// updateStats safely updates statistics.
+func (r *FileTypeRegistry) updateStats(fn func()) {
+	r.cacheMutex.Lock()
+	fn()
+	r.cacheMutex.Unlock()
+}
diff --git a/fileproc/collector.go b/fileproc/collector.go
index 72b4d2d..6091c98 100644
--- a/fileproc/collector.go
+++ b/fileproc/collector.go
@@ -4,6 +4,6 @@ package fileproc
 // CollectFiles scans the given root directory using the default walker (ProdWalker)
 // and returns a slice of file paths.
 func CollectFiles(root string) ([]string, error) {
-	var w Walker = ProdWalker{}
+	w := NewProdWalker()
 	return w.Walk(root)
 }
diff --git a/fileproc/collector_test.go b/fileproc/collector_test.go
index 2437403..55740c1 100644
--- a/fileproc/collector_test.go
+++ b/fileproc/collector_test.go
@@ -4,7 +4,7 @@ import (
 	"os"
 	"testing"
 
-	fileproc "github.com/ivuorinen/gibidify/fileproc"
+	"github.com/ivuorinen/gibidify/fileproc"
 )
 
 func TestCollectFilesWithFakeWalker(t *testing.T) {
diff --git a/fileproc/config.go b/fileproc/config.go
new file mode 100644
index 0000000..24d59e0
--- /dev/null
+++ b/fileproc/config.go
@@ -0,0 +1,40 @@
+package fileproc
+
+import "strings"
+
+// ApplyCustomExtensions applies custom extensions from configuration.
+func (r *FileTypeRegistry) ApplyCustomExtensions(customImages, customBinary []string, customLanguages map[string]string) {
+	// Add custom image extensions
+	r.addExtensions(customImages, r.AddImageExtension)
+
+	// Add custom binary extensions
+	r.addExtensions(customBinary, r.AddBinaryExtension)
+
+	// Add custom language mappings
+	for ext, lang := range customLanguages {
+		if ext != "" && lang != "" {
+			r.AddLanguageMapping(strings.ToLower(ext), lang)
+		}
+	}
+}
+
+// addExtensions is a helper to add multiple extensions.
+func (r *FileTypeRegistry) addExtensions(extensions []string, adder func(string)) {
+	for _, ext := range extensions {
+		if ext != "" {
+			adder(strings.ToLower(ext))
+		}
+	}
+}
+
+// ConfigureFromSettings applies configuration settings to the registry.
+// This function is called from main.go after config is loaded to avoid circular imports.
+func ConfigureFromSettings(
+	customImages, customBinary []string,
+	customLanguages map[string]string,
+	disabledImages, disabledBinary, disabledLanguages []string,
+) {
+	registry := GetDefaultRegistry()
+	registry.ApplyCustomExtensions(customImages, customBinary, customLanguages)
+	registry.DisableExtensions(disabledImages, disabledBinary, disabledLanguages)
+}
diff --git a/fileproc/detection.go b/fileproc/detection.go
new file mode 100644
index 0000000..f4e2929
--- /dev/null
+++ b/fileproc/detection.go
@@ -0,0 +1,99 @@
+package fileproc
+
+import "strings"
+
+// Package-level detection functions
+
+// IsImage checks if the file extension indicates an image file.
+func IsImage(filename string) bool {
+	return getRegistry().IsImage(filename)
+}
+
+// IsBinary checks if the file extension indicates a binary file.
+func IsBinary(filename string) bool {
+	return getRegistry().IsBinary(filename)
+}
+
+// GetLanguage returns the language identifier for the given filename based on its extension.
+func GetLanguage(filename string) string {
+	return getRegistry().GetLanguage(filename)
+}
+
+// Registry methods for detection
+
+// IsImage checks if the file extension indicates an image file.
+func (r *FileTypeRegistry) IsImage(filename string) bool {
+	result := r.getFileTypeResult(filename)
+	return result.IsImage
+}
+
+// IsBinary checks if the file extension indicates a binary file.
+func (r *FileTypeRegistry) IsBinary(filename string) bool {
+	result := r.getFileTypeResult(filename)
+	return result.IsBinary
+}
+
+// GetLanguage returns the language identifier for the given filename based on its extension.
+func (r *FileTypeRegistry) GetLanguage(filename string) string {
+	if len(filename) < minExtensionLength {
+		return ""
+	}
+	result := r.getFileTypeResult(filename)
+	return result.Language
+}
+
+// Extension management methods
+
+// AddImageExtension adds a new image extension to the registry.
+func (r *FileTypeRegistry) AddImageExtension(ext string) {
+	r.addExtension(ext, r.imageExts)
+}
+
+// AddBinaryExtension adds a new binary extension to the registry.
+func (r *FileTypeRegistry) AddBinaryExtension(ext string) {
+	r.addExtension(ext, r.binaryExts)
+}
+
+// AddLanguageMapping adds a new language mapping to the registry.
+func (r *FileTypeRegistry) AddLanguageMapping(ext, language string) {
+	r.languageMap[strings.ToLower(ext)] = language
+	r.invalidateCache()
+}
+
+// addExtension is a helper to add extensions to a map.
+func (r *FileTypeRegistry) addExtension(ext string, target map[string]bool) {
+	target[strings.ToLower(ext)] = true
+	r.invalidateCache()
+}
+
+// removeExtension is a helper to remove extensions from a map.
+func (r *FileTypeRegistry) removeExtension(ext string, target map[string]bool) {
+	delete(target, strings.ToLower(ext))
+}
+
+// DisableExtensions removes specified extensions from the registry.
+func (r *FileTypeRegistry) DisableExtensions(disabledImages, disabledBinary, disabledLanguages []string) {
+	// Disable image extensions
+	for _, ext := range disabledImages {
+		if ext != "" {
+			r.removeExtension(ext, r.imageExts)
+		}
+	}
+
+	// Disable binary extensions
+	for _, ext := range disabledBinary {
+		if ext != "" {
+			r.removeExtension(ext, r.binaryExts)
+		}
+	}
+
+	// Disable language extensions
+	for _, ext := range disabledLanguages {
+		if ext != "" {
+			delete(r.languageMap, strings.ToLower(ext))
+		}
+	}
+
+	// Invalidate cache after all modifications
+	r.invalidateCache()
+}
diff --git a/fileproc/extensions.go b/fileproc/extensions.go
new file mode 100644
index 0000000..602f107
--- /dev/null
+++ b/fileproc/extensions.go
@@ -0,0 +1,161 @@
+package fileproc
+
+// getImageExtensions returns the default image file extensions.
+func getImageExtensions() map[string]bool {
+	return map[string]bool{
+		".png":  true,
+		".jpg":  true,
+		".jpeg": true,
+		".gif":  true,
+		".bmp":  true,
+		".tiff": true,
+		".tif":  true,
+		".svg":  true,
+		".webp": true,
+		".ico":  true,
+	}
+}
+
+// getBinaryExtensions returns the default binary file extensions.
+func getBinaryExtensions() map[string]bool {
+	return map[string]bool{
+		// Executables and libraries
+		".exe":   true,
+		".dll":   true,
+		".so":    true,
+		".dylib": true,
+		".bin":   true,
+		".o":     true,
+		".a":     true,
+		".lib":   true,
+
+		// Compiled bytecode
+		".jar":   true,
+		".class": true,
+		".pyc":   true,
+		".pyo":   true,
+
+		// Data files
+		".dat":      true,
+		".db":       true,
+		".sqlite":   true,
+		".ds_store": true,
+
+		// Documents
+		".pdf": true,
+
+		// Archives
+		".zip": true,
+		".tar": true,
+		".gz":  true,
+		".bz2": true,
+		".xz":  true,
+		".7z":  true,
+		".rar": true,
+
+		// Fonts
+		".ttf":   true,
+		".otf":   true,
+		".woff":  true,
+		".woff2": true,
+
+		// Media files
+		".mp3":  true,
+		".mp4":  true,
+		".avi":  true,
+		".mov":  true,
+		".wmv":  true,
+		".flv":  true,
+		".webm": true,
+		".ogg":  true,
+		".wav":  true,
+		".flac": true,
+	}
+}
+
+// getLanguageMap returns the default language mappings.
+func getLanguageMap() map[string]string {
+	return map[string]string{
+		// Systems programming
+		".go":  "go",
+		".c":   "c",
+		".cpp": "cpp",
+		".h":   "c",
+		".hpp": "cpp",
+		".rs":  "rust",
+
+		// Scripting languages
+		".py":  "python",
+		".rb":  "ruby",
+		".pl":  "perl",
+		".lua": "lua",
+		".php": "php",
+
+		// Web technologies
+		".js":   "javascript",
+		".ts":   "typescript",
+		".jsx":  "javascript",
+		".tsx":  "typescript",
+		".html": "html",
+		".htm":  "html",
+		".css":  "css",
+		".scss": "scss",
+		".sass": "sass",
+		".less": "less",
+		".vue":  "vue",
+
+		// JVM languages
+		".java":  "java",
+		".scala": "scala",
+		".kt":    "kotlin",
+		".clj":   "clojure",
+
+		// .NET languages
+		".cs": "csharp",
+		".vb": "vbnet",
+		".fs": "fsharp",
+
+		// Apple platforms
+		".swift": "swift",
+		".m":     "objc",
+		".mm":    "objcpp",
+
+		// Shell scripts
+		".sh":   "bash",
+		".bash": "bash",
+		".zsh":  "zsh",
+		".fish": "fish",
+		".ps1":  "powershell",
+		".bat":  "batch",
+		".cmd":  "batch",
+
+		// Data formats
+		".json": "json",
+		".yaml": "yaml",
+		".yml":  "yaml",
+		".toml": "toml",
+		".xml":  "xml",
+		".sql":  "sql",
+
+		// Documentation
+		".md":  "markdown",
+		".rst": "rst",
+		".tex": "latex",
+
+		// Functional languages
+		".hs":  "haskell",
+		".ml":  "ocaml",
+		".mli": "ocaml",
+		".elm": "elm",
+		".ex":  "elixir",
+		".exs": "elixir",
+		".erl": "erlang",
+		".hrl": "erlang",
+
+		// Other languages
+		".r":    "r",
+		".dart": "dart",
+		".nim":  "nim",
+		".nims": "nim",
+	}
+}
diff --git a/fileproc/fake_walker.go b/fileproc/fake_walker.go
index fc156fd..f809717 100644
--- a/fileproc/fake_walker.go
+++ b/fileproc/fake_walker.go
@@ -3,8 +3,8 @@ package fileproc
 
 // FakeWalker implements Walker for testing purposes.
 type FakeWalker struct {
-	Files []string
 	Err   error
+	Files []string
 }
 
 // Walk returns predetermined file paths or an error, depending on FakeWalker's configuration.
diff --git a/fileproc/file_filters.go b/fileproc/file_filters.go
new file mode 100644
index 0000000..995d98f
--- /dev/null
+++ b/fileproc/file_filters.go
@@ -0,0 +1,55 @@
+package fileproc
+
+import (
+	"os"
+
+	"github.com/ivuorinen/gibidify/config"
+)
+
+// FileFilter defines filtering criteria for files and directories.
+type FileFilter struct {
+	ignoredDirs []string
+	sizeLimit   int64
+}
+
+// NewFileFilter creates a new file filter with current configuration.
+func NewFileFilter() *FileFilter {
+	return &FileFilter{
+		ignoredDirs: config.GetIgnoredDirectories(),
+		sizeLimit:   config.GetFileSizeLimit(),
+	}
+}
+
+// shouldSkipEntry determines if an entry should be skipped based on ignore rules and filters.
+func (f *FileFilter) shouldSkipEntry(entry os.DirEntry, fullPath string, rules []ignoreRule) bool {
+	if entry.IsDir() {
+		return f.shouldSkipDirectory(entry)
+	}
+
+	if f.shouldSkipFile(entry, fullPath) {
+		return true
+	}
+
+	return matchesIgnoreRules(fullPath, rules)
+}
+
+// shouldSkipDirectory checks if a directory should be skipped based on the ignored directories list.
+func (f *FileFilter) shouldSkipDirectory(entry os.DirEntry) bool {
+	for _, d := range f.ignoredDirs {
+		if entry.Name() == d {
+			return true
+		}
+	}
+	return false
+}
+
+// shouldSkipFile checks if a file should be skipped based on size limit and file type.
+func (f *FileFilter) shouldSkipFile(entry os.DirEntry, fullPath string) bool {
+	// Check if file exceeds the configured size limit.
+	if info, err := entry.Info(); err == nil && info.Size() > f.sizeLimit {
+		return true
+	}
+
+	// Apply the default filter to ignore binary and image files.
+	return IsBinary(fullPath) || IsImage(fullPath)
+}
diff --git a/fileproc/filetypes_test.go b/fileproc/filetypes_test.go
new file mode 100644
index 0000000..3053068
--- /dev/null
+++ b/fileproc/filetypes_test.go
@@ -0,0 +1,827 @@
+package fileproc
+
+import (
+	"fmt"
+	"sync"
+	"testing"
+)
+
+// TestFileTypeRegistry_ModificationMethods tests the modification methods of FileTypeRegistry.
+func TestFileTypeRegistry_ModificationMethods(t *testing.T) {
+	// Create a new registry instance for testing
+	registry := &FileTypeRegistry{
+		imageExts:   make(map[string]bool),
+		binaryExts:  make(map[string]bool),
+		languageMap: make(map[string]string),
+	}
+
+	// Test AddImageExtension
+	t.Run("AddImageExtension", func(t *testing.T) {
+		// Add a new image extension
+		registry.AddImageExtension(".webp")
+		if !registry.IsImage("test.webp") {
+			t.Errorf("Expected .webp to be recognized as image after adding")
+		}
+
+		// Test case insensitive addition
+		registry.AddImageExtension(".AVIF")
+		if !registry.IsImage("test.avif") {
+			t.Errorf("Expected .avif to be recognized as image after adding .AVIF")
+		}
+		if !registry.IsImage("test.AVIF") {
+			t.Errorf("Expected .AVIF to be recognized as image")
+		}
+
+		// Test with dot prefix
+		registry.AddImageExtension("heic")
+		if registry.IsImage("test.heic") {
+			t.Errorf("Expected extension without dot to not work")
+		}
+
+		// Test with proper dot prefix
+		registry.AddImageExtension(".heic")
+		if !registry.IsImage("test.heic") {
+			t.Errorf("Expected .heic to be recognized as image")
+		}
+	})
+
+	// Test AddBinaryExtension
+	t.Run("AddBinaryExtension", func(t *testing.T) {
+		// Add a new binary extension
+		registry.AddBinaryExtension(".custom")
+		if !registry.IsBinary("test.custom") {
+			t.Errorf("Expected .custom to be recognized as binary after adding")
+		}
+
+		// Test case insensitive addition
+		registry.AddBinaryExtension(".NEWBIN")
+		if !registry.IsBinary("test.newbin") {
+			t.Errorf("Expected .newbin to be recognized as binary after adding .NEWBIN")
+		}
+		if !registry.IsBinary("test.NEWBIN") {
+			t.Errorf("Expected .NEWBIN to be recognized as binary")
+		}
+
+		// Test overwriting existing extension
+		registry.AddBinaryExtension(".custom")
+		if !registry.IsBinary("test.custom") {
+			t.Errorf("Expected .custom to still be recognized as binary after re-adding")
+		}
+	})
+
+	// Test AddLanguageMapping
+	t.Run("AddLanguageMapping", func(t *testing.T) {
+		// Add a new language mapping
+		registry.AddLanguageMapping(".zig", "zig")
+		if registry.GetLanguage("test.zig") != "zig" {
+			t.Errorf("Expected .zig to map to 'zig', got '%s'", registry.GetLanguage("test.zig"))
+		}
+
+		// Test case insensitive addition
+		registry.AddLanguageMapping(".V", "vlang")
+		if registry.GetLanguage("test.v") != "vlang" {
+			t.Errorf("Expected .v to map to 'vlang' after adding .V, got '%s'", registry.GetLanguage("test.v"))
+		}
+		if registry.GetLanguage("test.V") != "vlang" {
+			t.Errorf("Expected .V to map to 'vlang', got '%s'", registry.GetLanguage("test.V"))
+		}
+
+		// Test overwriting existing mapping
+		registry.AddLanguageMapping(".zig", "ziglang")
+		if registry.GetLanguage("test.zig") != "ziglang" {
+			t.Errorf("Expected .zig to map to 'ziglang' after update, got '%s'", registry.GetLanguage("test.zig"))
+		}
+
+		// Test empty language
+		registry.AddLanguageMapping(".empty", "")
+		if registry.GetLanguage("test.empty") != "" {
+			t.Errorf("Expected .empty to map to empty string, got '%s'", registry.GetLanguage("test.empty"))
+		}
+	})
+}
+
+// TestFileTypeRegistry_LanguageDetection tests the language detection functionality.
+func TestFileTypeRegistry_LanguageDetection(t *testing.T) {
+	registry := GetDefaultRegistry()
+
+	tests := []struct {
+		filename string
+		expected string
+	}{
+		// Programming languages
+		{"main.go", "go"},
+		{"script.py", "python"},
+		{"app.js", "javascript"},
+		{"component.tsx", "typescript"},
+		{"service.ts", "typescript"},
+		{"App.java", "java"},
+		{"program.c", "c"},
+		{"program.cpp", "cpp"},
+		{"header.h", "c"},
+		{"header.hpp", "cpp"},
+		{"main.rs", "rust"},
+		{"script.rb", "ruby"},
+		{"index.php", "php"},
+		{"app.swift", "swift"},
+		{"MainActivity.kt", "kotlin"},
+		{"Main.scala", "scala"},
+		{"analysis.r", "r"},
+		{"ViewController.m", "objc"},
+		{"ViewController.mm", "objcpp"},
+		{"Program.cs", "csharp"},
+		{"Module.vb", "vbnet"},
+		{"program.fs", "fsharp"},
+		{"script.lua", "lua"},
+		{"script.pl", "perl"},
+
+		// Shell scripts
+		{"script.sh", "bash"},
+		{"script.bash", "bash"},
+		{"script.zsh", "zsh"},
+		{"script.fish", "fish"},
+		{"script.ps1", "powershell"},
+		{"script.bat", "batch"},
+		{"script.cmd", "batch"},
+
+		// Data and markup
+		{"query.sql", "sql"},
+		{"index.html", "html"},
+		{"page.htm", "html"},
+		{"data.xml", "xml"},
+		{"style.css", "css"},
+		{"style.scss", "scss"},
+		{"style.sass", "sass"},
+		{"style.less", "less"},
+		{"data.json", "json"},
+		{"config.yaml", "yaml"},
+		{"config.yml", "yaml"},
+		{"config.toml", "toml"},
+		{"README.md", "markdown"},
+		{"doc.rst", "rst"},
+		{"paper.tex", "latex"},
+
+		// Modern languages
+		{"main.dart", "dart"},
+		{"Main.elm", "elm"},
+		{"core.clj", "clojure"},
+		{"server.ex", "elixir"},
+		{"test.exs", "elixir"},
+		{"server.erl", "erlang"},
+		{"header.hrl", "erlang"},
+		{"main.hs", "haskell"},
+		{"module.ml", "ocaml"},
+		{"interface.mli", "ocaml"},
+		{"main.nim", "nim"},
+		{"config.nims", "nim"},
+
+		// Web frameworks
+		{"Component.vue", "vue"},
+		{"Component.jsx", "javascript"},
+
+		// Case sensitivity tests
+		{"MAIN.GO", "go"},
+		{"Script.PY", "python"},
+		{"APP.JS", "javascript"},
+
+		// Edge cases
+		{"", ""},             // Empty filename
+		{"a", ""},            // Too short (less than minExtensionLength)
+		{"noext", ""},        // No extension
+		{".hidden", ""},      // Hidden file with no name
+		{"file.", ""},        // Extension is just a dot
+		{"file.unknown", ""}, // Unknown extension
+		{"file.123", ""},     // Numeric extension
+		{"a.b", ""},          // Very short filename and extension
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.filename, func(t *testing.T) {
+			result := registry.GetLanguage(tt.filename)
+			if result != tt.expected {
+				t.Errorf("GetLanguage(%q) = %q, expected %q", tt.filename, result, tt.expected)
+			}
+		})
+	}
+}
+
+// TestFileTypeRegistry_ImageDetection tests the image detection functionality.
+func TestFileTypeRegistry_ImageDetection(t *testing.T) {
+	registry := GetDefaultRegistry()
+
+	tests := []struct {
+		filename string
+		expected bool
+	}{
+		// Common image formats
+		{"photo.png", true},
+		{"image.jpg", true},
+		{"picture.jpeg", true},
+		{"animation.gif", true},
+		{"bitmap.bmp", true},
+		{"image.tiff", true},
+		{"scan.tif", true},
+		{"vector.svg", true},
+		{"modern.webp", true},
+		{"favicon.ico", true},
+
+		// Case sensitivity tests
+		{"PHOTO.PNG", true},
+		{"IMAGE.JPG", true},
+		{"PICTURE.JPEG", true},
+
+		// Non-image files
+		{"document.txt", false},
+		{"script.js", false},
+		{"data.json", false},
+		{"archive.zip", false},
+		{"executable.exe", false},
+
+		// Edge cases
+		{"", false},              // Empty filename
+		{"image", false},         // No extension
+		{".png", true},           // Just extension
+		{"file.png.bak", false},  // Multiple extensions
+		{"image.unknown", false}, // Unknown extension
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.filename, func(t *testing.T) {
+			result := registry.IsImage(tt.filename)
+			if result != tt.expected {
+				t.Errorf("IsImage(%q) = %t, expected %t", tt.filename, result, tt.expected)
+			}
+		})
+	}
+}
+
+// TestFileTypeRegistry_BinaryDetection tests the binary detection functionality.
+func TestFileTypeRegistry_BinaryDetection(t *testing.T) {
+	registry := GetDefaultRegistry()
+
+	tests := []struct {
+		filename string
+		expected bool
+	}{
+		// Executable files
+		{"program.exe", true},
+		{"library.dll", true},
+		{"libfoo.so", true},
+		{"framework.dylib", true},
+		{"data.bin", true},
+
+		// Object and library files
+		{"object.o", true},
+		{"archive.a", true},
+		{"library.lib", true},
+		{"application.jar", true},
+		{"bytecode.class", true},
+		{"compiled.pyc", true},
+		{"optimized.pyo", true},
+
+		// System files
+		{".DS_Store", true},
+
+		// Document files (treated as binary)
+		{"document.pdf", true},
+
+		// Archive files
+		{"archive.zip", true},
+		{"backup.tar", true},
+		{"compressed.gz", true},
+		{"data.bz2", true},
+		{"package.xz", true},
+		{"archive.7z", true},
+		{"backup.rar", true},
+
+		// Font files
+		{"font.ttf", true},
+		{"font.otf", true},
+		{"font.woff", true},
+		{"font.woff2", true},
+
+		// Media files
+		{"song.mp3", true},
+		{"video.mp4", true},
+		{"movie.avi", true},
+		{"clip.mov", true},
+		{"video.wmv", true},
+		{"animation.flv", true},
+		{"modern.webm", true},
+		{"audio.ogg", true},
+		{"sound.wav", true},
+		{"music.flac", true},
+
+		// Database files
+		{"data.dat", true},
+		{"database.db", true},
+		{"app.sqlite", true},
+
+		// Case sensitivity tests
+		{"PROGRAM.EXE", true},
+		{"LIBRARY.DLL", true},
+
+		// Non-binary files
+		{"document.txt", false},
+		{"script.js", false},
+		{"data.json", false},
+		{"style.css", false},
+		{"page.html", false},
+
+		// Edge cases
+		{"", false},             // Empty filename
+		{"binary", false},       // No extension
+		{".exe", true},          // Just extension
+		{"file.exe.bak", false}, // Multiple extensions
+		{"file.unknown", false}, // Unknown extension
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.filename, func(t *testing.T) {
+			result := registry.IsBinary(tt.filename)
+			if result != tt.expected {
+				t.Errorf("IsBinary(%q) = %t, expected %t", tt.filename, result, tt.expected)
+			}
+		})
+	}
+}
+
+// TestFileTypeRegistry_DefaultRegistryConsistency tests that the default registry is consistent.
+func TestFileTypeRegistry_DefaultRegistryConsistency(t *testing.T) {
+	// Get registry multiple times and ensure it's the same instance
+	registry1 := GetDefaultRegistry()
+	registry2 := GetDefaultRegistry()
+	registry3 := getRegistry()
+
+	if registry1 != registry2 {
+		t.Error("GetDefaultRegistry() should return the same instance")
+	}
+	if registry1 != registry3 {
+		t.Error("getRegistry() should return the same instance as GetDefaultRegistry()")
+	}
+
+	// Test that global functions use the same registry
+	filename := "test.go"
+	if IsImage(filename) != registry1.IsImage(filename) {
+		t.Error("IsImage() global function should match registry method")
+	}
+	if IsBinary(filename) != registry1.IsBinary(filename) {
+		t.Error("IsBinary() global function should match registry method")
+	}
+	if GetLanguage(filename) != registry1.GetLanguage(filename) {
+		t.Error("GetLanguage() global function should match registry method")
+	}
+}
+
+// TestFileTypeRegistry_ThreadSafety tests the thread safety of the FileTypeRegistry.
+func TestFileTypeRegistry_ThreadSafety(t *testing.T) {
+	const numGoroutines = 100
+	const numOperationsPerGoroutine = 100
+
+	var wg sync.WaitGroup
+
+	// Test concurrent read operations
+	t.Run("ConcurrentReads", func(t *testing.T) {
+		for i := 0; i < numGoroutines; i++ {
+			wg.Add(1)
+			go func(id int) {
+				defer wg.Done()
+				registry := GetDefaultRegistry()
+
+				for j := 0; j < numOperationsPerGoroutine; j++ {
+					// Test various file detection operations
+					_ = registry.IsImage("test.png")
+					_ = registry.IsBinary("test.exe")
+					_ = registry.GetLanguage("test.go")
+
+					// Test global functions too
+					_ = IsImage("image.jpg")
+					_ = IsBinary("binary.dll")
+					_ = GetLanguage("script.py")
+				}
+			}(i)
+		}
+		wg.Wait()
+	})
+
+	// Test concurrent registry access (singleton creation)
+	t.Run("ConcurrentRegistryAccess", func(t *testing.T) {
+		// Reset the registry to test concurrent initialization
+		// Note: This is not safe in a real application, but needed for testing
+		registryOnce = sync.Once{}
+		registry = nil
+
+		registries := make([]*FileTypeRegistry, numGoroutines)
+
+		for i := 0; i < numGoroutines; i++ {
+			wg.Add(1)
+			go func(id int) {
+				defer wg.Done()
+				registries[id] = GetDefaultRegistry()
+			}(i)
+		}
+		wg.Wait()
+
+		// Verify all goroutines got the same registry instance
+		firstRegistry := registries[0]
+		for i := 1; i < numGoroutines; i++ {
+			if registries[i] != firstRegistry {
+				t.Errorf("Registry %d is different from registry 0", i)
+			}
+		}
+	})
+
+	// Test concurrent modifications on separate registry instances
+	t.Run("ConcurrentModifications", func(t *testing.T) {
+		// Create separate registry instances for each goroutine to test modification thread safety
+		for i := 0; i < numGoroutines; i++ {
+			wg.Add(1)
+			go func(id int) {
+				defer wg.Done()
+
+				// Create a new registry instance for this goroutine
+				registry := &FileTypeRegistry{
+					imageExts:   make(map[string]bool),
+					binaryExts:  make(map[string]bool),
+					languageMap: make(map[string]string),
+				}
+
+				for j := 0; j < numOperationsPerGoroutine; j++ {
+					// Add unique extensions for this goroutine
+					extSuffix := fmt.Sprintf("_%d_%d", id, j)
+
+					registry.AddImageExtension(".img" + extSuffix)
+					registry.AddBinaryExtension(".bin" + extSuffix)
+					registry.AddLanguageMapping(".lang"+extSuffix, "lang"+extSuffix)
+
+					// Verify the additions worked
+					if !registry.IsImage("test.img" + extSuffix) {
+						t.Errorf("Failed to add image extension .img%s", extSuffix)
+					}
+					if !registry.IsBinary("test.bin" + extSuffix) {
+						t.Errorf("Failed to add binary extension .bin%s", extSuffix)
+					}
+					if registry.GetLanguage("test.lang"+extSuffix) != "lang"+extSuffix {
+						t.Errorf("Failed to add language mapping .lang%s", extSuffix)
+					}
+				}
+			}(i)
+		}
+		wg.Wait()
+	})
+}
+
+// TestFileTypeRegistry_EdgeCases tests edge cases and boundary conditions.
+func TestFileTypeRegistry_EdgeCases(t *testing.T) {
+	registry := GetDefaultRegistry()
+
+	// Test various edge cases for filename handling
+	edgeCases := []struct {
+		name     string
+		filename string
+		desc     string
+	}{
+		{"empty", "", "empty filename"},
+		{"single_char", "a", "single character filename"},
+		{"just_dot", ".", "just a dot"},
+		{"double_dot", "..", "double dot"},
+		{"hidden_file", ".hidden", "hidden file"},
+		{"hidden_with_ext", ".hidden.txt", "hidden file with extension"},
+		{"multiple_dots", "file.tar.gz", "multiple extensions"},
+		{"trailing_dot", "file.", "trailing dot"},
+		{"unicode", "файл.txt", "unicode filename"},
+		{"spaces", "my file.txt", "filename with spaces"},
+		{"special_chars", "file@#$.txt", "filename with special characters"},
+		{"very_long", "very_long_filename_with_many_characters_in_it.extension", "very long filename"},
+		{"no_basename", ".gitignore", "dotfile with no basename"},
+		{"case_mixed", "FiLe.ExT", "mixed case"},
+	}
+
+	for _, tc := range edgeCases {
+		t.Run(tc.name, func(t *testing.T) {
+			// These should not panic
+			_ = registry.IsImage(tc.filename)
+			_ = registry.IsBinary(tc.filename)
+			_ = registry.GetLanguage(tc.filename)
+
+			// Global functions should also not panic
+			_ = IsImage(tc.filename)
+			_ = IsBinary(tc.filename)
+			_ = GetLanguage(tc.filename)
+		})
+	}
+}
+
+// TestFileTypeRegistry_MinimumExtensionLength tests the minimum extension length requirement.
+func TestFileTypeRegistry_MinimumExtensionLength(t *testing.T) {
+	registry := GetDefaultRegistry()
+
+	tests := []struct {
+		filename string
+		expected string
+	}{
+		{"", ""},            // Empty filename
+		{"a", ""},           // Single character (less than minExtensionLength)
+		{"ab", ""},          // Two characters, no extension
+		{"a.b", ""},         // Extension too short, but filename too short anyway
+		{"ab.c", "c"},       // Valid: filename >= minExtensionLength and .c is valid extension
+		{"a.go", "go"},      // Valid extension
+		{"ab.py", "python"}, // Valid extension
+		{"a.unknown", ""},   // Valid length but unknown extension
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.filename, func(t *testing.T) {
+			result := registry.GetLanguage(tt.filename)
+			if result != tt.expected {
+				t.Errorf("GetLanguage(%q) = %q, expected %q", tt.filename, result, tt.expected)
+			}
+		})
+	}
+}
+
+// BenchmarkFileTypeRegistry tests performance of the registry operations.
+func BenchmarkFileTypeRegistry_IsImage(b *testing.B) {
+	registry := GetDefaultRegistry()
+	filename := "test.png"
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = registry.IsImage(filename)
+	}
+}
+
+func BenchmarkFileTypeRegistry_IsBinary(b *testing.B) {
+	registry := GetDefaultRegistry()
+	filename := "test.exe"
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = registry.IsBinary(filename)
+	}
+}
+
+func BenchmarkFileTypeRegistry_GetLanguage(b *testing.B) {
+	registry := GetDefaultRegistry()
+	filename := "test.go"
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = registry.GetLanguage(filename)
+	}
+}
+
+func BenchmarkFileTypeRegistry_GlobalFunctions(b *testing.B) {
+	filename := "test.go"
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = IsImage(filename)
+		_ = IsBinary(filename)
+		_ = GetLanguage(filename)
+	}
+}
+
+func BenchmarkFileTypeRegistry_ConcurrentAccess(b *testing.B) {
+	filename := "test.go"
+
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			_ = IsImage(filename)
+			_ = IsBinary(filename)
+			_ = GetLanguage(filename)
+		}
+	})
+}
+
+// TestFileTypeRegistry_Configuration tests the configuration functionality.
+func TestFileTypeRegistry_Configuration(t *testing.T) {
+	// Create a new registry instance for testing
+	registry := &FileTypeRegistry{
+		imageExts:   make(map[string]bool),
+		binaryExts:  make(map[string]bool),
+		languageMap: make(map[string]string),
+	}
+
+	// Test ApplyCustomExtensions
+	t.Run("ApplyCustomExtensions", func(t *testing.T) {
+		customImages := []string{".webp", ".avif", ".heic"}
+		customBinary := []string{".custom", ".mybin"}
+		customLanguages := map[string]string{
+			".zig":  "zig",
+			".odin": "odin",
+			".v":    "vlang",
+		}
+
+		registry.ApplyCustomExtensions(customImages, customBinary, customLanguages)
+
+		// Test custom image extensions
+		for _, ext := range customImages {
+			if !registry.IsImage("test" + ext) {
+				t.Errorf("Expected %s to be recognized as image", ext)
+			}
+		}
+
+		// Test custom binary extensions
+		for _, ext := range customBinary {
+			if !registry.IsBinary("test" + ext) {
+				t.Errorf("Expected %s to be recognized as binary", ext)
+			}
+		}
+
+		// Test custom language mappings
+		for ext, expectedLang := range customLanguages {
+			if lang := registry.GetLanguage("test" + ext); lang != expectedLang {
+				t.Errorf("Expected %s to map to %s, got %s", ext, expectedLang, lang)
+			}
+		}
+	})
+
+	// Test DisableExtensions
+	t.Run("DisableExtensions", func(t *testing.T) {
+		// Add some extensions first
+		registry.AddImageExtension(".png")
+		registry.AddImageExtension(".jpg")
+		registry.AddBinaryExtension(".exe")
+		registry.AddBinaryExtension(".dll")
+		registry.AddLanguageMapping(".go", "go")
+		registry.AddLanguageMapping(".py", "python")
+
+		// Verify they work
+		if !registry.IsImage("test.png") {
+			t.Error("Expected .png to be image before disabling")
+		}
+		if !registry.IsBinary("test.exe") {
+			t.Error("Expected .exe to be binary before disabling")
+		}
+		if registry.GetLanguage("test.go") != "go" {
+			t.Error("Expected .go to map to go before disabling")
+		}
+
+		// Disable some extensions
+		disabledImages := []string{".png"}
+		disabledBinary := []string{".exe"}
+		disabledLanguages := []string{".go"}
+
+		registry.DisableExtensions(disabledImages, disabledBinary, disabledLanguages)
+
+		// Test that disabled extensions no longer work
+		if registry.IsImage("test.png") {
+			t.Error("Expected .png to not be image after disabling")
+		}
+		if registry.IsBinary("test.exe") {
+			t.Error("Expected .exe to not be binary after disabling")
+		}
+		if registry.GetLanguage("test.go") != "" {
+			t.Error("Expected .go to not map to language after disabling")
+		}
+
+		// Test that non-disabled extensions still work
+		if !registry.IsImage("test.jpg") {
+			t.Error("Expected .jpg to still be image after disabling .png")
+		}
+		if !registry.IsBinary("test.dll") {
+			t.Error("Expected .dll to still be binary after disabling .exe")
+		}
+		if registry.GetLanguage("test.py") != "python" {
+			t.Error("Expected .py to still map to python after disabling .go")
+		}
+	})
+
+	// Test empty values handling
+	t.Run("EmptyValuesHandling", func(t *testing.T) {
+		registry := &FileTypeRegistry{
+			imageExts:   make(map[string]bool),
+			binaryExts:  make(map[string]bool),
+			languageMap: make(map[string]string),
+		}
+
+		// Test with empty values
+		customImages := []string{"", ".valid", ""}
+		customBinary := []string{"", ".valid"}
+		customLanguages := map[string]string{
+			"":       "invalid",
+			".valid": "",
+			".good":  "good",
+		}
+
+		registry.ApplyCustomExtensions(customImages, customBinary, customLanguages)
+
+		// Only valid entries should be added
+		if registry.IsImage("test.") {
+			t.Error("Expected empty extension to not be added as image")
+		}
+		if !registry.IsImage("test.valid") {
+			t.Error("Expected .valid to be added as image")
+		}
+		if registry.IsBinary("test.") {
+			t.Error("Expected empty extension to not be added as binary")
+		}
+		if !registry.IsBinary("test.valid") {
+			t.Error("Expected .valid to be added as binary")
+		}
+		if registry.GetLanguage("test.") != "" {
+			t.Error("Expected empty extension to not be added as language")
+		}
+		if registry.GetLanguage("test.valid") != "" {
+			t.Error("Expected .valid with empty language to not be added")
+		}
+		if registry.GetLanguage("test.good") != "good" {
+			t.Error("Expected .good to map to good")
+		}
+	})
+
+	// Test case insensitive handling
+	t.Run("CaseInsensitiveHandling", func(t *testing.T) {
+		registry := &FileTypeRegistry{
+			imageExts:   make(map[string]bool),
+			binaryExts:  make(map[string]bool),
+			languageMap: make(map[string]string),
+		}
+
+		customImages := []string{".WEBP", ".Avif"}
+		customBinary := []string{".CUSTOM", ".MyBin"}
+		customLanguages := map[string]string{
+			".ZIG":  "zig",
+			".Odin": "odin",
+		}
+
+		registry.ApplyCustomExtensions(customImages, customBinary, customLanguages)
+
+		// Test that both upper and lower case work
+		if !registry.IsImage("test.webp") {
+			t.Error("Expected .webp (lowercase) to work after adding .WEBP")
+		}
+		if !registry.IsImage("test.WEBP") {
+			t.Error("Expected .WEBP (uppercase) to work")
+		}
+		if !registry.IsBinary("test.custom") {
+			t.Error("Expected .custom (lowercase) to work after adding .CUSTOM")
+		}
+		if !registry.IsBinary("test.CUSTOM") {
+			t.Error("Expected .CUSTOM (uppercase) to work")
+		}
+		if registry.GetLanguage("test.zig") != "zig" {
+			t.Error("Expected .zig (lowercase) to work after adding .ZIG")
+		}
+		if registry.GetLanguage("test.ZIG") != "zig" {
+			t.Error("Expected .ZIG (uppercase) to work")
+		}
+	})
+}
+
+// TestConfigureFromSettings tests the global configuration function.
+func TestConfigureFromSettings(t *testing.T) {
+	// Reset registry to ensure clean state
+	registryOnce = sync.Once{}
+	registry = nil
+
+	// Test configuration application
+	customImages := []string{".webp", ".avif"}
+	customBinary := []string{".custom"}
+	customLanguages := map[string]string{".zig": "zig"}
+	disabledImages := []string{".gif"}   // Disable default extension
+	disabledBinary := []string{".exe"}   // Disable default extension
+	disabledLanguages := []string{".rb"} // Disable default extension
+
+	ConfigureFromSettings(
+		customImages,
+		customBinary,
+		customLanguages,
+		disabledImages,
+		disabledBinary,
+		disabledLanguages,
+	)
+
+	// Test that custom extensions work
+	if !IsImage("test.webp") {
+		t.Error("Expected custom image extension .webp to work")
+	}
+	if !IsBinary("test.custom") {
+		t.Error("Expected custom binary extension .custom to work")
+	}
+	if GetLanguage("test.zig") != "zig" {
+		t.Error("Expected custom language .zig to work")
+	}
+
+	// Test that disabled extensions don't work
+	if IsImage("test.gif") {
+		t.Error("Expected disabled image extension .gif to not work")
+	}
+	if IsBinary("test.exe") {
+		t.Error("Expected disabled binary extension .exe to not work")
+	}
+	if GetLanguage("test.rb") != "" {
+		t.Error("Expected disabled language extension .rb to not work")
+	}
+
+	// Test that non-disabled defaults still work
+	if !IsImage("test.png") {
+		t.Error("Expected non-disabled image extension .png to still work")
+	}
+	if !IsBinary("test.dll") {
+		t.Error("Expected non-disabled binary extension .dll to still work")
+	}
+	if GetLanguage("test.go") != "go" {
+		t.Error("Expected non-disabled language extension .go to still work")
+	}
+}
diff --git a/fileproc/formats.go b/fileproc/formats.go
new file mode 100644
index 0000000..86795af
--- /dev/null
+++ b/fileproc/formats.go
@@ -0,0 +1,28 @@
+package fileproc
+
+// FileData represents a single file's path and content.
+type FileData struct {
+	Path     string `json:"path"     yaml:"path"`
+	Content  string `json:"content"  yaml:"content"`
+	Language string `json:"language" yaml:"language"`
+}
+
+// OutputData represents the full output structure.
+type OutputData struct {
+	Prefix string     `json:"prefix,omitempty" yaml:"prefix,omitempty"`
+	Suffix string     `json:"suffix,omitempty" yaml:"suffix,omitempty"`
+	Files  []FileData `json:"files"            yaml:"files"`
+}
+
+// FormatWriter defines the interface for format-specific writers.
+type FormatWriter interface {
+	Start(prefix, suffix string) error
+	WriteFile(req WriteRequest) error
+	Close() error
+}
+
+// detectLanguage tries to infer the code block language from the file extension.
+func detectLanguage(filePath string) string {
+	registry := GetDefaultRegistry()
+	return registry.GetLanguage(filePath)
+}
diff --git a/fileproc/ignore_rules.go b/fileproc/ignore_rules.go
new file mode 100644
index 0000000..827a0f0
--- /dev/null
+++ b/fileproc/ignore_rules.go
@@ -0,0 +1,66 @@
+package fileproc
+
+import (
+	"os"
+	"path/filepath"
+
+	ignore "github.com/sabhiram/go-gitignore"
+)
+
+// ignoreRule holds an ignore matcher along with the base directory where it was loaded.
+type ignoreRule struct {
+	gi   *ignore.GitIgnore
+	base string
+}
+
+// loadIgnoreRules loads ignore rules from the current directory and combines them with parent rules.
+func loadIgnoreRules(currentDir string, parentRules []ignoreRule) []ignoreRule {
+	// Pre-allocate for parent rules plus possible .gitignore and .ignore
+	const expectedIgnoreFiles = 2
+	rules := make([]ignoreRule, 0, len(parentRules)+expectedIgnoreFiles)
+	rules = append(rules, parentRules...)
+
+	// Check for .gitignore and .ignore files in the current directory.
+	for _, fileName := range []string{".gitignore", ".ignore"} {
+		if rule := tryLoadIgnoreFile(currentDir, fileName); rule != nil {
+			rules = append(rules, *rule)
+		}
+	}
+
+	return rules
+}
+
+// tryLoadIgnoreFile attempts to load an ignore file from the given directory.
+func tryLoadIgnoreFile(dir, fileName string) *ignoreRule {
+	ignorePath := filepath.Join(dir, fileName)
+	if info, err := os.Stat(ignorePath); err == nil && !info.IsDir() {
+		if gi, err := ignore.CompileIgnoreFile(ignorePath); err == nil {
+			return &ignoreRule{
+				base: dir,
+				gi:   gi,
+			}
+		}
+	}
+	return nil
+}
+
+// matchesIgnoreRules checks if a path matches any of the ignore rules.
+func matchesIgnoreRules(fullPath string, rules []ignoreRule) bool {
+	for _, rule := range rules {
+		if matchesRule(fullPath, rule) {
+			return true
+		}
+	}
+	return false
+}
+
+// matchesRule checks if a path matches a specific ignore rule.
+func matchesRule(fullPath string, rule ignoreRule) bool {
+	// Compute the path relative to the base where the ignore rule was defined.
+	rel, err := filepath.Rel(rule.base, fullPath)
+	if err != nil {
+		return false
+	}
+	// If the rule matches, skip this entry.
+	return rule.gi.MatchesPath(rel)
+}
diff --git a/fileproc/json_writer.go b/fileproc/json_writer.go
new file mode 100644
index 0000000..57bc6d9
--- /dev/null
+++ b/fileproc/json_writer.go
@@ -0,0 +1,188 @@
+package fileproc
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+// JSONWriter handles JSON format output with streaming support.
+type JSONWriter struct {
+	outFile   *os.File
+	firstFile bool
+}
+
+// NewJSONWriter creates a new JSON writer.
+func NewJSONWriter(outFile *os.File) *JSONWriter {
+	return &JSONWriter{
+		outFile:   outFile,
+		firstFile: true,
+	}
+}
+
+// Start writes the JSON header.
+func (w *JSONWriter) Start(prefix, suffix string) error {
+	// Start JSON structure
+	if _, err := w.outFile.WriteString(`{"prefix":"`); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON start")
+	}
+
+	// Write escaped prefix
+	escapedPrefix := escapeJSONString(prefix)
+	if _, err := w.outFile.WriteString(escapedPrefix); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON prefix")
+	}
+
+	if _, err := w.outFile.WriteString(`","suffix":"`); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON middle")
+	}
+
+	// Write escaped suffix
+	escapedSuffix := escapeJSONString(suffix)
+	if _, err := w.outFile.WriteString(escapedSuffix); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON suffix")
+	}
+
+	if _, err := w.outFile.WriteString(`","files":[`); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON files start")
+	}
+
+	return nil
+}
+
+// WriteFile writes a file entry in JSON format.
+func (w *JSONWriter) WriteFile(req WriteRequest) error {
+	if !w.firstFile {
+		if _, err := w.outFile.WriteString(","); err != nil {
+			return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON separator")
+		}
+	}
+	w.firstFile = false
+
+	if req.IsStream {
+		return w.writeStreaming(req)
+	}
+	return w.writeInline(req)
+}
+
+// Close writes the JSON footer.
+func (w *JSONWriter) Close() error {
+	// Close JSON structure
+	if _, err := w.outFile.WriteString("]}"); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON end")
+	}
+	return nil
+}
+
+// writeStreaming writes a large file as JSON in streaming chunks.
+func (w *JSONWriter) writeStreaming(req WriteRequest) error {
+	defer w.closeReader(req.Reader, req.Path)
+
+	language := detectLanguage(req.Path)
+
+	// Write file start
+	escapedPath := escapeJSONString(req.Path)
+	if _, err := fmt.Fprintf(w.outFile, `{"path":"%s","language":"%s","content":"`, escapedPath, language); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON file start").WithFilePath(req.Path)
+	}
+
+	// Stream content with JSON escaping
+	if err := w.streamJSONContent(req.Reader, req.Path); err != nil {
+		return err
+	}
+
+	// Write file end
+	if _, err := w.outFile.WriteString(`"}`); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON file end").WithFilePath(req.Path)
+	}
+
+	return nil
+}
+
+// writeInline writes a small file directly as JSON.
+func (w *JSONWriter) writeInline(req WriteRequest) error {
+	language := detectLanguage(req.Path)
+	fileData := FileData{
+		Path:     req.Path,
+		Content:  req.Content,
+		Language: language,
+	}
+
+	encoded, err := json.Marshal(fileData)
+	if err != nil {
+		return utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingEncode, "failed to marshal JSON").WithFilePath(req.Path)
+	}
+
+	if _, err := w.outFile.Write(encoded); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON file").WithFilePath(req.Path)
+	}
+	return nil
+}
+
+// streamJSONContent streams content with JSON escaping.
+func (w *JSONWriter) streamJSONContent(reader io.Reader, path string) error {
+	buf := make([]byte, StreamChunkSize)
+	for {
+		n, err := reader.Read(buf)
+		if n > 0 {
+			escaped := escapeJSONString(string(buf[:n]))
+			if _, writeErr := w.outFile.WriteString(escaped); writeErr != nil {
+				return utils.WrapError(writeErr, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write JSON chunk").WithFilePath(path)
+			}
+		}
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIORead, "failed to read JSON chunk").WithFilePath(path)
+		}
+	}
+	return nil
+}
+
+// closeReader safely closes a reader if it implements io.Closer.
+func (w *JSONWriter) closeReader(reader io.Reader, path string) {
+	if closer, ok := reader.(io.Closer); ok {
+		if err := closer.Close(); err != nil {
+			utils.LogError(
+				"Failed to close file reader",
+				utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOClose, "failed to close file reader").WithFilePath(path),
+			)
+		}
+	}
+}
+
+// escapeJSONString escapes a string for JSON output.
+func escapeJSONString(s string) string {
+	// Use json.Marshal to properly escape the string, then remove the quotes
+	escaped, _ := json.Marshal(s)
+	return string(escaped[1 : len(escaped)-1]) // Remove surrounding quotes
+}
+
+// startJSONWriter handles JSON format output with streaming support.
+func startJSONWriter(outFile *os.File, writeCh <-chan WriteRequest, done chan<- struct{}, prefix, suffix string) {
+	defer close(done)
+
+	writer := NewJSONWriter(outFile)
+
+	// Start writing
+	if err := writer.Start(prefix, suffix); err != nil {
+		utils.LogError("Failed to write JSON start", err)
+		return
+	}
+
+	// Process files
+	for req := range writeCh {
+		if err := writer.WriteFile(req); err != nil {
+			utils.LogError("Failed to write JSON file", err)
+		}
+	}
+
+	// Close writer
+	if err := writer.Close(); err != nil {
+		utils.LogError("Failed to write JSON end", err)
+	}
+}
diff --git a/fileproc/markdown_writer.go b/fileproc/markdown_writer.go
new file mode 100644
index 0000000..56e5fdf
--- /dev/null
+++ b/fileproc/markdown_writer.go
@@ -0,0 +1,139 @@
+package fileproc
+
+import (
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+// MarkdownWriter handles markdown format output with streaming support.
+type MarkdownWriter struct {
+	outFile *os.File
+}
+
+// NewMarkdownWriter creates a new markdown writer.
+func NewMarkdownWriter(outFile *os.File) *MarkdownWriter {
+	return &MarkdownWriter{outFile: outFile}
+}
+
+// Start writes the markdown header.
+func (w *MarkdownWriter) Start(prefix, suffix string) error {
+	if prefix != "" {
+		if _, err := fmt.Fprintf(w.outFile, "# %s\n\n", prefix); err != nil {
+			return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write prefix")
+		}
+	}
+	return nil
+}
+
+// WriteFile writes a file entry in markdown format.
+func (w *MarkdownWriter) WriteFile(req WriteRequest) error {
+	if req.IsStream {
+		return w.writeStreaming(req)
+	}
+	return w.writeInline(req)
+}
+
+// Close writes the markdown footer.
+func (w *MarkdownWriter) Close(suffix string) error {
+	if suffix != "" {
+		if _, err := fmt.Fprintf(w.outFile, "\n# %s\n", suffix); err != nil {
+			return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write suffix")
+		}
+	}
+	return nil
+}
+
+// writeStreaming writes a large file in streaming chunks.
+func (w *MarkdownWriter) writeStreaming(req WriteRequest) error {
+	defer w.closeReader(req.Reader, req.Path)
+
+	language := detectLanguage(req.Path)
+
+	// Write file header
+	if _, err := fmt.Fprintf(w.outFile, "## File: `%s`\n```%s\n", req.Path, language); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write file header").WithFilePath(req.Path)
+	}
+
+	// Stream file content in chunks
+	if err := w.streamContent(req.Reader, req.Path); err != nil {
+		return err
+	}
+
+	// Write file footer
+	if _, err := w.outFile.WriteString("\n```\n\n"); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write file footer").WithFilePath(req.Path)
+	}
+
+	return nil
+}
+
+// writeInline writes a small file directly from content.
+func (w *MarkdownWriter) writeInline(req WriteRequest) error {
+	language := detectLanguage(req.Path)
+	formatted := fmt.Sprintf("## File: `%s`\n```%s\n%s\n```\n\n", req.Path, language, req.Content)
+
+	if _, err := w.outFile.WriteString(formatted); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write inline content").WithFilePath(req.Path)
+	}
+	return nil
+}
+
+// streamContent streams file content in chunks.
+func (w *MarkdownWriter) streamContent(reader io.Reader, path string) error {
+	buf := make([]byte, StreamChunkSize)
+	for {
+		n, err := reader.Read(buf)
+		if n > 0 {
+			if _, writeErr := w.outFile.Write(buf[:n]); writeErr != nil {
+				return utils.WrapError(writeErr, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write chunk").WithFilePath(path)
+			}
+		}
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIORead, "failed to read chunk").WithFilePath(path)
+		}
+	}
+	return nil
+}
+
+// closeReader safely closes a reader if it implements io.Closer.
+func (w *MarkdownWriter) closeReader(reader io.Reader, path string) {
+	if closer, ok := reader.(io.Closer); ok {
+		if err := closer.Close(); err != nil {
+			utils.LogError(
+				"Failed to close file reader",
+				utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOClose, "failed to close file reader").WithFilePath(path),
+			)
+		}
+	}
+}
+
+// startMarkdownWriter handles markdown format output with streaming support.
+func startMarkdownWriter(outFile *os.File, writeCh <-chan WriteRequest, done chan<- struct{}, prefix, suffix string) {
+	defer close(done)
+
+	writer := NewMarkdownWriter(outFile)
+
+	// Start writing
+	if err := writer.Start(prefix, suffix); err != nil {
+		utils.LogError("Failed to write markdown prefix", err)
+		return
+	}
+
+	// Process files
+	for req := range writeCh {
+		if err := writer.WriteFile(req); err != nil {
+			utils.LogError("Failed to write markdown file", err)
+		}
+	}
+
+	// Close writer
+	if err := writer.Close(suffix); err != nil {
+		utils.LogError("Failed to write markdown suffix", err)
+	}
+}
diff --git a/fileproc/processor.go b/fileproc/processor.go
index 97e0761..335c364 100644
--- a/fileproc/processor.go
+++ b/fileproc/processor.go
@@ -3,34 +3,157 @@ package fileproc
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
+	"strings"
 
-	"github.com/sirupsen/logrus"
+	"github.com/ivuorinen/gibidify/config"
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+const (
+	// StreamChunkSize is the size of chunks when streaming large files (64KB).
+	StreamChunkSize = 65536
+	// StreamThreshold is the file size above which we use streaming (1MB).
+	StreamThreshold = 1048576
+	// MaxMemoryBuffer is the maximum memory to use for buffering content (10MB).
+	MaxMemoryBuffer = 10485760
 )
 
 // WriteRequest represents the content to be written.
 type WriteRequest struct {
-	Path    string
-	Content string
+	Path     string
+	Content  string
+	IsStream bool
+	Reader   io.Reader
+}
+
+// FileProcessor handles file processing operations.
+type FileProcessor struct {
+	rootPath  string
+	sizeLimit int64
+}
+
+// NewFileProcessor creates a new file processor.
+func NewFileProcessor(rootPath string) *FileProcessor {
+	return &FileProcessor{
+		rootPath:  rootPath,
+		sizeLimit: config.GetFileSizeLimit(),
+	}
 }
 
 // ProcessFile reads the file at filePath and sends a formatted output to outCh.
+// It automatically chooses between loading the entire file or streaming based on file size.
 func ProcessFile(filePath string, outCh chan<- WriteRequest, rootPath string) {
-	content, err := os.ReadFile(filePath)
+	processor := NewFileProcessor(rootPath)
+	processor.Process(filePath, outCh)
+}
+
+// Process handles file processing with the configured settings.
+func (p *FileProcessor) Process(filePath string, outCh chan<- WriteRequest) {
+	// Validate file
+	fileInfo, err := p.validateFile(filePath)
 	if err != nil {
-		logrus.Errorf("Failed to read file %s: %v", filePath, err)
+		return // Error already logged
+	}
+
+	// Get relative path
+	relPath := p.getRelativePath(filePath)
+
+	// Choose processing strategy based on file size
+	if fileInfo.Size() <= StreamThreshold {
+		p.processInMemory(filePath, relPath, outCh)
+	} else {
+		p.processStreaming(filePath, relPath, outCh)
+	}
+}
+
+// validateFile checks if the file can be processed.
+func (p *FileProcessor) validateFile(filePath string) (os.FileInfo, error) {
+	fileInfo, err := os.Stat(filePath)
+	if err != nil {
+		structErr := utils.WrapError(err, utils.ErrorTypeFileSystem, utils.CodeFSAccess, "failed to stat file").WithFilePath(filePath)
+		utils.LogErrorf(structErr, "Failed to stat file %s", filePath)
+		return nil, err
+	}
+
+	// Check size limit
+	if fileInfo.Size() > p.sizeLimit {
+		utils.LogErrorf(
+			utils.NewStructuredError(
+				utils.ErrorTypeValidation,
+				utils.CodeValidationSize,
+				fmt.Sprintf("file size (%d bytes) exceeds limit (%d bytes)", fileInfo.Size(), p.sizeLimit),
+			).WithFilePath(filePath).WithContext("file_size", fileInfo.Size()).WithContext("size_limit", p.sizeLimit),
+			"Skipping large file %s", filePath,
+		)
+		return nil, fmt.Errorf("file too large")
+	}
+
+	return fileInfo, nil
+}
+
+// getRelativePath computes the path relative to rootPath.
+func (p *FileProcessor) getRelativePath(filePath string) string {
+	relPath, err := filepath.Rel(p.rootPath, filePath)
+	if err != nil {
+		return filePath // Fallback
+	}
+	return relPath
+}
+
+// processInMemory loads the entire file into memory (for small files).
+func (p *FileProcessor) processInMemory(filePath, relPath string, outCh chan<- WriteRequest) {
+	content, err := os.ReadFile(filePath) // #nosec G304 - filePath is validated by walker
+	if err != nil {
+		structErr := utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingFileRead, "failed to read file").WithFilePath(filePath)
+		utils.LogErrorf(structErr, "Failed to read file %s", filePath)
 		return
 	}
 
-	// Compute path relative to rootPath, so /a/b/c/d.c becomes c/d.c
-	relPath, err := filepath.Rel(rootPath, filePath)
-	if err != nil {
-		// Fallback if something unexpected happens
-		relPath = filePath
+	outCh <- WriteRequest{
+		Path:     relPath,
+		Content:  p.formatContent(relPath, string(content)),
+		IsStream: false,
+	}
+}
+
+// processStreaming creates a streaming reader for large files.
+func (p *FileProcessor) processStreaming(filePath, relPath string, outCh chan<- WriteRequest) {
+	reader := p.createStreamReader(filePath, relPath)
+	if reader == nil {
+		return // Error already logged
 	}
 
-	// Format: separator, then relative path, then content
-	formatted := fmt.Sprintf("\n---\n%s\n%s\n", relPath, string(content))
-	outCh <- WriteRequest{Path: relPath, Content: formatted}
+	outCh <- WriteRequest{
+		Path:     relPath,
+		Content:  "", // Empty since content is in Reader
+		IsStream: true,
+		Reader:   reader,
+	}
+}
+
+// createStreamReader creates a reader that combines header and file content.
+func (p *FileProcessor) createStreamReader(filePath, relPath string) io.Reader {
+	file, err := os.Open(filePath) // #nosec G304 - filePath is validated by walker
+	if err != nil {
+		structErr := utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingFileRead, "failed to open file for streaming").WithFilePath(filePath)
+		utils.LogErrorf(structErr, "Failed to open file for streaming %s", filePath)
+		return nil
+	}
+	// Note: file will be closed by the writer
+
+	header := p.formatHeader(relPath)
+	return io.MultiReader(header, file)
+}
+
+// formatContent formats the file content with header.
+func (p *FileProcessor) formatContent(relPath, content string) string {
+	return fmt.Sprintf("\n---\n%s\n%s\n", relPath, content)
+}
+
+// formatHeader creates a reader for the file header.
+func (p *FileProcessor) formatHeader(relPath string) io.Reader {
+	return strings.NewReader(fmt.Sprintf("\n---\n%s\n", relPath))
 }
diff --git a/fileproc/processor_test.go b/fileproc/processor_test.go
index d1c1077..e825399 100644
--- a/fileproc/processor_test.go
+++ b/fileproc/processor_test.go
@@ -6,12 +6,15 @@ import (
 	"sync"
 	"testing"
 
-	fileproc "github.com/ivuorinen/gibidify/fileproc"
+	"github.com/ivuorinen/gibidify/fileproc"
+	"github.com/ivuorinen/gibidify/testutil"
 )
 
 func TestProcessFile(t *testing.T) {
+	// Reset and load default config to ensure proper file size limits
+	testutil.ResetViperConfig(t, "")
 	// Create a temporary file with known content.
-	tmpFile, err := os.CreateTemp("", "testfile")
+	tmpFile, err := os.CreateTemp(t.TempDir(), "testfile")
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/fileproc/registry.go b/fileproc/registry.go
new file mode 100644
index 0000000..1ea6f74
--- /dev/null
+++ b/fileproc/registry.go
@@ -0,0 +1,107 @@
+// Package fileproc provides file processing utilities.
+package fileproc
+
+import (
+	"path/filepath"
+	"strings"
+	"sync"
+)
+
+const minExtensionLength = 2
+
+var (
+	registry     *FileTypeRegistry
+	registryOnce sync.Once
+)
+
+// FileTypeRegistry manages file type detection and classification.
+type FileTypeRegistry struct {
+	imageExts   map[string]bool
+	binaryExts  map[string]bool
+	languageMap map[string]string
+
+	// Cache for frequent lookups to avoid repeated string operations
+	extCache     map[string]string         // filename -> normalized extension
+	resultCache  map[string]FileTypeResult // extension -> cached result
+	cacheMutex   sync.RWMutex
+	maxCacheSize int
+
+	// Performance statistics
+	stats RegistryStats
+}
+
+// RegistryStats tracks performance metrics for the registry.
+type RegistryStats struct {
+	TotalLookups   uint64
+	CacheHits      uint64
+	CacheMisses    uint64
+	CacheEvictions uint64
+}
+
+// FileTypeResult represents cached file type detection results.
+type FileTypeResult struct {
+	IsImage   bool
+	IsBinary  bool
+	Language  string
+	Extension string
+}
+
+// initRegistry initializes the default file type registry with common extensions.
+func initRegistry() *FileTypeRegistry {
+	return &FileTypeRegistry{
+		imageExts:    getImageExtensions(),
+		binaryExts:   getBinaryExtensions(),
+		languageMap:  getLanguageMap(),
+		extCache:     make(map[string]string, 1000),        // Cache for extension normalization
+		resultCache:  make(map[string]FileTypeResult, 500), // Cache for type results
+		maxCacheSize: 500,
+	}
+}
+
+// getRegistry returns the singleton file type registry, creating it if necessary.
+func getRegistry() *FileTypeRegistry {
+	registryOnce.Do(func() {
+		registry = initRegistry()
+	})
+	return registry
+}
+
+// GetDefaultRegistry returns the default file type registry.
+func GetDefaultRegistry() *FileTypeRegistry {
+	return getRegistry()
+}
+
+// GetStats returns a copy of the current registry statistics.
+func (r *FileTypeRegistry) GetStats() RegistryStats {
+	r.cacheMutex.RLock()
+	defer r.cacheMutex.RUnlock()
+	return r.stats
+}
+
+// GetCacheInfo returns current cache size information.
+func (r *FileTypeRegistry) GetCacheInfo() (extCacheSize, resultCacheSize, maxCacheSize int) {
+	r.cacheMutex.RLock()
+	defer r.cacheMutex.RUnlock()
+	return len(r.extCache), len(r.resultCache), r.maxCacheSize
+}
+
+// ResetRegistryForTesting resets the registry to its initial state.
+// This function should only be used in tests.
+func ResetRegistryForTesting() {
+	registryOnce = sync.Once{}
+	registry = nil
+}
+
+// normalizeExtension extracts and normalizes the file extension.
+func normalizeExtension(filename string) string {
+	return strings.ToLower(filepath.Ext(filename))
+}
+
+// isSpecialFile checks if the filename matches special cases like .DS_Store.
+func isSpecialFile(filename string, extensions map[string]bool) bool {
+	if filepath.Ext(filename) == "" {
+		basename := strings.ToLower(filepath.Base(filename))
+		return extensions[basename]
+	}
+	return false
+}
diff --git a/fileproc/walker.go b/fileproc/walker.go
index f4bb776..58f9e64 100644
--- a/fileproc/walker.go
+++ b/fileproc/walker.go
@@ -4,10 +4,8 @@ package fileproc
 import (
 	"os"
 	"path/filepath"
-	"strings"
 
-	"github.com/ivuorinen/gibidify/config"
-	ignore "github.com/sabhiram/go-gitignore"
+	"github.com/ivuorinen/gibidify/utils"
 )
 
 // Walker defines an interface for scanning directories.
@@ -18,22 +16,25 @@ type Walker interface {
 // ProdWalker implements Walker using a custom directory walker that
 // respects .gitignore and .ignore files, configuration-defined ignore directories,
 // and ignores binary and image files by default.
-type ProdWalker struct{}
+type ProdWalker struct {
+	filter *FileFilter
+}
 
-// ignoreRule holds an ignore matcher along with the base directory where it was loaded.
-type ignoreRule struct {
-	base string
-	gi   *ignore.GitIgnore
+// NewProdWalker creates a new production walker with current configuration.
+func NewProdWalker() *ProdWalker {
+	return &ProdWalker{
+		filter: NewFileFilter(),
+	}
 }
 
 // Walk scans the given root directory recursively and returns a slice of file paths
 // that are not ignored based on .gitignore/.ignore files, the configuration, or the default binary/image filter.
-func (pw ProdWalker) Walk(root string) ([]string, error) {
-	absRoot, err := filepath.Abs(root)
+func (w *ProdWalker) Walk(root string) ([]string, error) {
+	absRoot, err := utils.GetAbsolutePath(root)
 	if err != nil {
-		return nil, err
+		return nil, utils.WrapError(err, utils.ErrorTypeFileSystem, utils.CodeFSPathResolution, "failed to resolve root path").WithFilePath(root)
 	}
-	return walkDir(absRoot, absRoot, []ignoreRule{})
+	return w.walkDir(absRoot, []ignoreRule{})
 }
 
 // walkDir recursively walks the directory tree starting at currentDir.
@@ -41,122 +42,34 @@ func (pw ProdWalker) Walk(root string) ([]string, error) {
 // appends the corresponding rules to the inherited list. Each file/directory is
 // then checked against the accumulated ignore rules, the configuration's list of ignored directories,
 // and a default filter that ignores binary and image files.
-func walkDir(root string, currentDir string, parentRules []ignoreRule) ([]string, error) {
+func (w *ProdWalker) walkDir(currentDir string, parentRules []ignoreRule) ([]string, error) {
 	var results []string
 
 	entries, err := os.ReadDir(currentDir)
 	if err != nil {
-		return nil, err
+		return nil, utils.WrapError(err, utils.ErrorTypeFileSystem, utils.CodeFSAccess, "failed to read directory").WithFilePath(currentDir)
 	}
 
-	// Start with the parent's ignore rules.
-	rules := make([]ignoreRule, len(parentRules))
-	copy(rules, parentRules)
-
-	// Check for .gitignore and .ignore files in the current directory.
-	for _, fileName := range []string{".gitignore", ".ignore"} {
-		ignorePath := filepath.Join(currentDir, fileName)
-		if info, err := os.Stat(ignorePath); err == nil && !info.IsDir() {
-			gi, err := ignore.CompileIgnoreFile(ignorePath)
-			if err == nil {
-				rules = append(rules, ignoreRule{
-					base: currentDir,
-					gi:   gi,
-				})
-			}
-		}
-	}
-
-	// Get the list of directories to ignore from configuration.
-	ignoredDirs := config.GetIgnoredDirectories()
-	sizeLimit := config.GetFileSizeLimit() // e.g., 5242880 for 5 MB
+	rules := loadIgnoreRules(currentDir, parentRules)
 
 	for _, entry := range entries {
 		fullPath := filepath.Join(currentDir, entry.Name())
 
-		// For directories, check if its name is in the config ignore list.
-		if entry.IsDir() {
-			for _, d := range ignoredDirs {
-				if entry.Name() == d {
-					// Skip this directory entirely.
-					goto SkipEntry
-				}
-			}
-		} else {
-			// Check if file exceeds the configured size limit.
-			info, err := entry.Info()
-			if err == nil && info.Size() > sizeLimit {
-				goto SkipEntry
-			}
-
-			// For files, apply the default filter to ignore binary and image files.
-			if isBinaryOrImage(fullPath) {
-				goto SkipEntry
-			}
+		if w.filter.shouldSkipEntry(entry, fullPath, rules) {
+			continue
 		}
 
-		// Check accumulated ignore rules.
-		for _, rule := range rules {
-			// Compute the path relative to the base where the ignore rule was defined.
-			rel, err := filepath.Rel(rule.base, fullPath)
-			if err != nil {
-				continue
-			}
-			// If the rule matches, skip this entry.
-			if rule.gi.MatchesPath(rel) {
-				goto SkipEntry
-			}
-		}
-
-		// If not ignored, then process the entry.
+		// Process entry
 		if entry.IsDir() {
-			subFiles, err := walkDir(root, fullPath, rules)
+			subFiles, err := w.walkDir(fullPath, rules)
 			if err != nil {
-				return nil, err
+				return nil, utils.WrapError(err, utils.ErrorTypeProcessing, utils.CodeProcessingTraversal, "failed to traverse subdirectory").WithFilePath(fullPath)
 			}
 			results = append(results, subFiles...)
 		} else {
 			results = append(results, fullPath)
 		}
-	SkipEntry:
-		continue
 	}
 
 	return results, nil
 }
-
-// isBinaryOrImage checks if a file should be considered binary or an image based on its extension.
-// The check is case-insensitive.
-func isBinaryOrImage(filePath string) bool {
-	ext := strings.ToLower(filepath.Ext(filePath))
-	// Common image file extensions.
-	imageExtensions := map[string]bool{
-		".png":  true,
-		".jpg":  true,
-		".jpeg": true,
-		".gif":  true,
-		".bmp":  true,
-		".tiff": true,
-		".ico":  true,
-		".svg":  true,
-		".webp": true,
-	}
-	// Common binary file extensions.
-	binaryExtensions := map[string]bool{
-		".exe":      true,
-		".dll":      true,
-		".so":       true,
-		".bin":      true,
-		".dat":      true,
-		".zip":      true,
-		".tar":      true,
-		".gz":       true,
-		".7z":       true,
-		".rar":      true,
-		".DS_Store": true,
-	}
-	if imageExtensions[ext] || binaryExtensions[ext] {
-		return true
-	}
-	return false
-}
diff --git a/fileproc/walker_test.go b/fileproc/walker_test.go
index f684947..dfee038 100644
--- a/fileproc/walker_test.go
+++ b/fileproc/walker_test.go
@@ -1,64 +1,42 @@
 package fileproc_test
 
 import (
-	"os"
 	"path/filepath"
 	"testing"
 
-	"github.com/ivuorinen/gibidify/config"
-	fileproc "github.com/ivuorinen/gibidify/fileproc"
 	"github.com/spf13/viper"
+
+	"github.com/ivuorinen/gibidify/fileproc"
+	"github.com/ivuorinen/gibidify/testutil"
 )
 
 func TestProdWalkerWithIgnore(t *testing.T) {
 	// Create a temporary directory structure.
-	rootDir, err := os.MkdirTemp("", "walker_test_root")
-	if err != nil {
-		t.Fatalf("Failed to create temp root directory: %v", err)
-	}
-	defer func() {
-		if err := os.RemoveAll(rootDir); err != nil {
-			t.Fatalf("cleanup failed: %v", err)
-		}
-	}()
+	rootDir := t.TempDir()
 
-	subDir := filepath.Join(rootDir, "vendor")
-	if err := os.Mkdir(subDir, 0755); err != nil {
-		t.Fatalf("Failed to create subDir: %v", err)
-	}
+	subDir := testutil.CreateTestDirectory(t, rootDir, "vendor")
 
 	// Write sample files
-	filePaths := []string{
-		filepath.Join(rootDir, "file1.go"),
-		filepath.Join(rootDir, "file2.txt"),
-		filepath.Join(subDir, "file_in_vendor.txt"), // should be ignored
-	}
-	for _, fp := range filePaths {
-		if err := os.WriteFile(fp, []byte("content"), 0644); err != nil {
-			t.Fatalf("Failed to write file %s: %v", fp, err)
-		}
-	}
+	testutil.CreateTestFiles(t, rootDir, []testutil.FileSpec{
+		{Name: "file1.go", Content: "content"},
+		{Name: "file2.txt", Content: "content"},
+	})
+	testutil.CreateTestFile(t, subDir, "file_in_vendor.txt", []byte("content")) // should be ignored
 
 	// .gitignore that ignores *.txt and itself
 	gitignoreContent := `*.txt
 .gitignore
 `
-	gitignorePath := filepath.Join(rootDir, ".gitignore")
-	if err := os.WriteFile(gitignorePath, []byte(gitignoreContent), 0644); err != nil {
-		t.Fatalf("Failed to write .gitignore: %v", err)
-	}
+	testutil.CreateTestFile(t, rootDir, ".gitignore", []byte(gitignoreContent))
 
 	// Initialize config to ignore "vendor" directory
-	viper.Reset()
-	config.LoadConfig()
+	testutil.ResetViperConfig(t, "")
 	viper.Set("ignoreDirectories", []string{"vendor"})
 
 	// Run walker
-	var w fileproc.Walker = fileproc.ProdWalker{}
+	w := fileproc.NewProdWalker()
 	found, err := w.Walk(rootDir)
-	if err != nil {
-		t.Fatalf("Walk returned error: %v", err)
-	}
+	testutil.MustSucceed(t, err, "walking directory")
 
 	// We expect only file1.go to appear
 	if len(found) != 1 {
@@ -70,38 +48,24 @@ func TestProdWalkerWithIgnore(t *testing.T) {
 }
 
 func TestProdWalkerBinaryCheck(t *testing.T) {
-	rootDir, err := os.MkdirTemp("", "walker_test_bincheck")
-	if err != nil {
-		t.Fatalf("Failed to create temp root directory: %v", err)
-	}
-	defer func() {
-		if err := os.RemoveAll(rootDir); err != nil {
-			t.Fatalf("cleanup failed: %v", err)
-		}
-	}()
+	rootDir := t.TempDir()
 
-	// Create a mock binary file
-	binFile := filepath.Join(rootDir, "somefile.exe")
-	if err := os.WriteFile(binFile, []byte("fake-binary-content"), 0644); err != nil {
-		t.Fatalf("Failed to write file %s: %v", binFile, err)
-	}
-
-	// Create a normal file
-	normalFile := filepath.Join(rootDir, "keep.go")
-	if err := os.WriteFile(normalFile, []byte("package main"), 0644); err != nil {
-		t.Fatalf("Failed to write file %s: %v", normalFile, err)
-	}
+	// Create test files
+	testutil.CreateTestFiles(t, rootDir, []testutil.FileSpec{
+		{Name: "somefile.exe", Content: "fake-binary-content"},
+		{Name: "keep.go", Content: "package main"},
+	})
 
 	// Reset and load default config
-	viper.Reset()
-	config.LoadConfig()
+	testutil.ResetViperConfig(t, "")
+
+	// Reset FileTypeRegistry to ensure clean state
+	fileproc.ResetRegistryForTesting()
 
 	// Run walker
-	var w fileproc.Walker = fileproc.ProdWalker{}
+	w := fileproc.NewProdWalker()
 	found, err := w.Walk(rootDir)
-	if err != nil {
-		t.Fatalf("Walk returned error: %v", err)
-	}
+	testutil.MustSucceed(t, err, "walking directory")
 
 	// Only "keep.go" should be returned
 	if len(found) != 1 {
@@ -113,34 +77,17 @@ func TestProdWalkerBinaryCheck(t *testing.T) {
 }
 
 func TestProdWalkerSizeLimit(t *testing.T) {
-	rootDir, err := os.MkdirTemp("", "walker_test_sizelimit")
-	if err != nil {
-		t.Fatalf("Failed to create temp root directory: %v", err)
-	}
-	defer func() {
-		if err := os.RemoveAll(rootDir); err != nil {
-			t.Fatalf("cleanup failed: %v", err)
-		}
-	}()
+	rootDir := t.TempDir()
 
-	// Create a file exceeding the size limit
-	largeFilePath := filepath.Join(rootDir, "largefile.txt")
+	// Create test files
 	largeFileData := make([]byte, 6*1024*1024) // 6 MB
-	if err := os.WriteFile(largeFilePath, largeFileData, 0644); err != nil {
-		t.Fatalf("Failed to write large file: %v", err)
-	}
-
-	// Create a small file
-	smallFilePath := filepath.Join(rootDir, "smallfile.go")
-	if err := os.WriteFile(smallFilePath, []byte("package main"), 0644); err != nil {
-		t.Fatalf("Failed to write small file: %v", err)
-	}
+	testutil.CreateTestFile(t, rootDir, "largefile.txt", largeFileData)
+	testutil.CreateTestFile(t, rootDir, "smallfile.go", []byte("package main"))
 
 	// Reset and load default config, which sets size limit to 5 MB
-	viper.Reset()
-	config.LoadConfig()
+	testutil.ResetViperConfig(t, "")
 
-	var w fileproc.Walker = fileproc.ProdWalker{}
+	w := fileproc.NewProdWalker()
 	found, err := w.Walk(rootDir)
 	if err != nil {
 		t.Fatalf("Walk returned error: %v", err)
diff --git a/fileproc/writer.go b/fileproc/writer.go
index b530b25..8858b0e 100644
--- a/fileproc/writer.go
+++ b/fileproc/writer.go
@@ -1,101 +1,29 @@
 // Package fileproc provides a writer for the output of the file processor.
-//
-// The StartWriter function writes the output in the specified format.
-// The formatMarkdown function formats the output in Markdown format.
-// The detectLanguage function tries to infer the code block language from the file extension.
-// The OutputData struct represents the full output structure.
-// The FileData struct represents a single file's path and content.
 package fileproc
 
 import (
-	"encoding/json"
 	"fmt"
 	"os"
 
-	"github.com/sirupsen/logrus"
-	"gopkg.in/yaml.v3"
+	"github.com/ivuorinen/gibidify/utils"
 )
 
-// FileData represents a single file's path and content.
-type FileData struct {
-	Path    string `json:"path" yaml:"path"`
-	Content string `json:"content" yaml:"content"`
-}
-
-// OutputData represents the full output structure.
-type OutputData struct {
-	Prefix string     `json:"prefix,omitempty" yaml:"prefix,omitempty"`
-	Files  []FileData `json:"files" yaml:"files"`
-	Suffix string     `json:"suffix,omitempty" yaml:"suffix,omitempty"`
-}
-
-// StartWriter writes the output in the specified format.
-func StartWriter(outFile *os.File, writeCh <-chan WriteRequest, done chan<- struct{}, format string, prefix, suffix string) {
-	var files []FileData
-
-	// Read from channel until closed
-	for req := range writeCh {
-		files = append(files, FileData(req))
-	}
-
-	// Create output struct
-	output := OutputData{Prefix: prefix, Files: files, Suffix: suffix}
-
-	// Serialize based on format
-	var outputData []byte
-	var err error
-
+// StartWriter writes the output in the specified format with memory optimization.
+func StartWriter(outFile *os.File, writeCh <-chan WriteRequest, done chan<- struct{}, format, prefix, suffix string) {
 	switch format {
-	case "json":
-		outputData, err = json.MarshalIndent(output, "", "  ")
-	case "yaml":
-		outputData, err = yaml.Marshal(output)
 	case "markdown":
-		outputData = []byte(formatMarkdown(output))
+		startMarkdownWriter(outFile, writeCh, done, prefix, suffix)
+	case "json":
+		startJSONWriter(outFile, writeCh, done, prefix, suffix)
+	case "yaml":
+		startYAMLWriter(outFile, writeCh, done, prefix, suffix)
 	default:
-		err = fmt.Errorf("unsupported format: %s", format)
-	}
-
-	if err != nil {
-		logrus.Errorf("Error encoding output: %v", err)
+		err := utils.NewStructuredError(
+			utils.ErrorTypeValidation,
+			utils.CodeValidationFormat,
+			fmt.Sprintf("unsupported format: %s", format),
+		).WithContext("format", format)
+		utils.LogError("Failed to encode output", err)
 		close(done)
-		return
-	}
-
-	// Write to file
-	if _, err := outFile.Write(outputData); err != nil {
-		logrus.Errorf("Error writing to file: %v", err)
-	}
-
-	close(done)
-}
-
-func formatMarkdown(output OutputData) string {
-	markdown := "# " + output.Prefix + "\n\n"
-
-	for _, file := range output.Files {
-		markdown += fmt.Sprintf("## File: `%s`\n```%s\n%s\n```\n\n", file.Path, detectLanguage(file.Path), file.Content)
-	}
-
-	markdown += "# " + output.Suffix
-	return markdown
-}
-
-// detectLanguage tries to infer code block language from file extension.
-func detectLanguage(filename string) string {
-	if len(filename) < 3 {
-		return ""
-	}
-	switch {
-	case len(filename) >= 3 && filename[len(filename)-3:] == ".go":
-		return "go"
-	case len(filename) >= 3 && filename[len(filename)-3:] == ".py":
-		return "python"
-	case len(filename) >= 2 && filename[len(filename)-2:] == ".c":
-		return "c"
-	case len(filename) >= 3 && filename[len(filename)-3:] == ".js":
-		return "javascript"
-	default:
-		return ""
 	}
 }
diff --git a/fileproc/writer_test.go b/fileproc/writer_test.go
index 2c3eaa4..0320e23 100644
--- a/fileproc/writer_test.go
+++ b/fileproc/writer_test.go
@@ -7,8 +7,9 @@ import (
 	"sync"
 	"testing"
 
-	fileproc "github.com/ivuorinen/gibidify/fileproc"
 	"gopkg.in/yaml.v3"
+
+	"github.com/ivuorinen/gibidify/fileproc"
 )
 
 func TestStartWriter_Formats(t *testing.T) {
@@ -18,107 +19,109 @@ func TestStartWriter_Formats(t *testing.T) {
 		format      string
 		expectError bool
 	}{
-		{
-			name:        "JSON format",
-			format:      "json",
-			expectError: false,
-		},
-		{
-			name:        "YAML format",
-			format:      "yaml",
-			expectError: false,
-		},
-		{
-			name:        "Markdown format",
-			format:      "markdown",
-			expectError: false,
-		},
-		{
-			name:        "Invalid format",
-			format:      "invalid",
-			expectError: true,
-		},
+		{"JSON format", "json", false},
+		{"YAML format", "yaml", false},
+		{"Markdown format", "markdown", false},
+		{"Invalid format", "invalid", true},
 	}
 
 	for _, tc := range tests {
 		t.Run(tc.name, func(t *testing.T) {
-			outFile, err := os.CreateTemp("", "gibidify_test_output")
-			if err != nil {
-				t.Fatalf("Failed to create temp file: %v", err)
-			}
-			defer func() {
-				if err := outFile.Close(); err != nil {
-					t.Errorf("close temp file: %v", err)
-				}
-				if err := os.Remove(outFile.Name()); err != nil {
-					t.Errorf("remove temp file: %v", err)
-				}
-			}()
-
-			// Prepare channels
-			writeCh := make(chan fileproc.WriteRequest, 2)
-			doneCh := make(chan struct{})
-
-			// Write a couple of sample requests
-			writeCh <- fileproc.WriteRequest{Path: "sample.go", Content: "package main"}
-			writeCh <- fileproc.WriteRequest{Path: "example.py", Content: "def foo(): pass"}
-			close(writeCh)
-
-			// Start the writer
-			var wg sync.WaitGroup
-			wg.Add(1)
-			go func() {
-				defer wg.Done()
-				fileproc.StartWriter(outFile, writeCh, doneCh, tc.format, "PREFIX", "SUFFIX")
-			}()
-
-			// Wait until writer signals completion
-			wg.Wait()
-			<-doneCh // make sure all writes finished
-
-			// Read output
-			data, err := os.ReadFile(outFile.Name())
-			if err != nil {
-				t.Fatalf("Error reading output file: %v", err)
-			}
-
+			data := runWriterTest(t, tc.format)
 			if tc.expectError {
-				// For an invalid format, we expect StartWriter to log an error
-				// and produce no content or minimal content. There's no official
-				// error returned, so check if it's empty or obviously incorrect.
-				if len(data) != 0 {
-					t.Errorf("Expected no output for invalid format, got:\n%s", data)
-				}
+				verifyErrorOutput(t, data)
 			} else {
-				// Valid format: check basic properties in the output
-				content := string(data)
-				switch tc.format {
-				case "json":
-					// Quick parse check
-					var outStruct fileproc.OutputData
-					if err := json.Unmarshal(data, &outStruct); err != nil {
-						t.Errorf("JSON unmarshal failed: %v", err)
-					}
-				case "yaml":
-					var outStruct fileproc.OutputData
-					if err := yaml.Unmarshal(data, &outStruct); err != nil {
-						t.Errorf("YAML unmarshal failed: %v", err)
-					}
-				case "markdown":
-					// Check presence of code fences or "## File: ..."
-					if !strings.Contains(content, "```") {
-						t.Error("Expected markdown code fences not found")
-					}
-				}
-
-				// Prefix and suffix checks (common to JSON, YAML, markdown)
-				if !strings.Contains(string(data), "PREFIX") {
-					t.Errorf("Missing prefix in output: %s", data)
-				}
-				if !strings.Contains(string(data), "SUFFIX") {
-					t.Errorf("Missing suffix in output: %s", data)
-				}
+				verifyValidOutput(t, data, tc.format)
+				verifyPrefixSuffix(t, data)
 			}
 		})
 	}
 }
+
+// runWriterTest executes the writer with the given format and returns the output data.
+func runWriterTest(t *testing.T, format string) []byte {
+	t.Helper()
+	outFile, err := os.CreateTemp(t.TempDir(), "gibidify_test_output")
+	if err != nil {
+		t.Fatalf("Failed to create temp file: %v", err)
+	}
+	defer func() {
+		if closeErr := outFile.Close(); closeErr != nil {
+			t.Errorf("close temp file: %v", closeErr)
+		}
+		if removeErr := os.Remove(outFile.Name()); removeErr != nil {
+			t.Errorf("remove temp file: %v", removeErr)
+		}
+	}()
+
+	// Prepare channels
+	writeCh := make(chan fileproc.WriteRequest, 2)
+	doneCh := make(chan struct{})
+
+	// Write a couple of sample requests
+	writeCh <- fileproc.WriteRequest{Path: "sample.go", Content: "package main"}
+	writeCh <- fileproc.WriteRequest{Path: "example.py", Content: "def foo(): pass"}
+	close(writeCh)
+
+	// Start the writer
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		fileproc.StartWriter(outFile, writeCh, doneCh, format, "PREFIX", "SUFFIX")
+	}()
+
+	// Wait until writer signals completion
+	wg.Wait()
+	<-doneCh // make sure all writes finished
+
+	// Read output
+	data, err := os.ReadFile(outFile.Name())
+	if err != nil {
+		t.Fatalf("Error reading output file: %v", err)
+	}
+
+	return data
+}
+
+// verifyErrorOutput checks that error cases produce no output.
+func verifyErrorOutput(t *testing.T, data []byte) {
+	t.Helper()
+	if len(data) != 0 {
+		t.Errorf("Expected no output for invalid format, got:\n%s", data)
+	}
+}
+
+// verifyValidOutput checks format-specific output validity.
+func verifyValidOutput(t *testing.T, data []byte, format string) {
+	t.Helper()
+	content := string(data)
+	switch format {
+	case "json":
+		var outStruct fileproc.OutputData
+		if err := json.Unmarshal(data, &outStruct); err != nil {
+			t.Errorf("JSON unmarshal failed: %v", err)
+		}
+	case "yaml":
+		var outStruct fileproc.OutputData
+		if err := yaml.Unmarshal(data, &outStruct); err != nil {
+			t.Errorf("YAML unmarshal failed: %v", err)
+		}
+	case "markdown":
+		if !strings.Contains(content, "```") {
+			t.Error("Expected markdown code fences not found")
+		}
+	}
+}
+
+// verifyPrefixSuffix checks that output contains expected prefix and suffix.
+func verifyPrefixSuffix(t *testing.T, data []byte) {
+	t.Helper()
+	content := string(data)
+	if !strings.Contains(content, "PREFIX") {
+		t.Errorf("Missing prefix in output: %s", data)
+	}
+	if !strings.Contains(content, "SUFFIX") {
+		t.Errorf("Missing suffix in output: %s", data)
+	}
+}
diff --git a/fileproc/yaml_writer.go b/fileproc/yaml_writer.go
new file mode 100644
index 0000000..3ea60f2
--- /dev/null
+++ b/fileproc/yaml_writer.go
@@ -0,0 +1,148 @@
+package fileproc
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"github.com/ivuorinen/gibidify/utils"
+)
+
+// YAMLWriter handles YAML format output with streaming support.
+type YAMLWriter struct {
+	outFile *os.File
+}
+
+// NewYAMLWriter creates a new YAML writer.
+func NewYAMLWriter(outFile *os.File) *YAMLWriter {
+	return &YAMLWriter{outFile: outFile}
+}
+
+// Start writes the YAML header.
+func (w *YAMLWriter) Start(prefix, suffix string) error {
+	// Write YAML header
+	if _, err := fmt.Fprintf(w.outFile, "prefix: %s\nsuffix: %s\nfiles:\n", yamlQuoteString(prefix), yamlQuoteString(suffix)); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write YAML header")
+	}
+	return nil
+}
+
+// WriteFile writes a file entry in YAML format.
+func (w *YAMLWriter) WriteFile(req WriteRequest) error {
+	if req.IsStream {
+		return w.writeStreaming(req)
+	}
+	return w.writeInline(req)
+}
+
+// Close writes the YAML footer (no footer needed for YAML).
+func (w *YAMLWriter) Close() error {
+	return nil
+}
+
+// writeStreaming writes a large file as YAML in streaming chunks.
+func (w *YAMLWriter) writeStreaming(req WriteRequest) error {
+	defer w.closeReader(req.Reader, req.Path)
+
+	language := detectLanguage(req.Path)
+
+	// Write YAML file entry start
+	if _, err := fmt.Fprintf(w.outFile, "  - path: %s\n    language: %s\n    content: |\n", yamlQuoteString(req.Path), language); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write YAML file start").WithFilePath(req.Path)
+	}
+
+	// Stream content with YAML indentation
+	return w.streamYAMLContent(req.Reader, req.Path)
+}
+
+// writeInline writes a small file directly as YAML.
+func (w *YAMLWriter) writeInline(req WriteRequest) error {
+	language := detectLanguage(req.Path)
+	fileData := FileData{
+		Path:     req.Path,
+		Content:  req.Content,
+		Language: language,
+	}
+
+	// Write YAML entry
+	if _, err := fmt.Fprintf(w.outFile, "  - path: %s\n    language: %s\n    content: |\n", yamlQuoteString(fileData.Path), fileData.Language); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write YAML entry start").WithFilePath(req.Path)
+	}
+
+	// Write indented content
+	lines := strings.Split(fileData.Content, "\n")
+	for _, line := range lines {
+		if _, err := fmt.Fprintf(w.outFile, "      %s\n", line); err != nil {
+			return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write YAML content line").WithFilePath(req.Path)
+		}
+	}
+
+	return nil
+}
+
+// streamYAMLContent streams content with YAML indentation.
+func (w *YAMLWriter) streamYAMLContent(reader io.Reader, path string) error {
+	scanner := bufio.NewScanner(reader)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if _, err := fmt.Fprintf(w.outFile, "      %s\n", line); err != nil {
+			return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOWrite, "failed to write YAML line").WithFilePath(path)
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIORead, "failed to scan YAML content").WithFilePath(path)
+	}
+	return nil
+}
+
+// closeReader safely closes a reader if it implements io.Closer.
+func (w *YAMLWriter) closeReader(reader io.Reader, path string) {
+	if closer, ok := reader.(io.Closer); ok {
+		if err := closer.Close(); err != nil {
+			utils.LogError(
+				"Failed to close file reader",
+				utils.WrapError(err, utils.ErrorTypeIO, utils.CodeIOClose, "failed to close file reader").WithFilePath(path),
+			)
+		}
+	}
+}
+
+// yamlQuoteString quotes a string for YAML output if needed.
+func yamlQuoteString(s string) string {
+	if s == "" {
+		return `""`
+	}
+	// Simple YAML quoting - use double quotes if string contains special characters
+	if strings.ContainsAny(s, "\n\r\t:\"'\\") {
+		return fmt.Sprintf(`"%s"`, strings.ReplaceAll(s, `"`, `\"`))
+	}
+	return s
+}
+
+// startYAMLWriter handles YAML format output with streaming support.
+func startYAMLWriter(outFile *os.File, writeCh <-chan WriteRequest, done chan<- struct{}, prefix, suffix string) {
+	defer close(done)
+
+	writer := NewYAMLWriter(outFile)
+
+	// Start writing
+	if err := writer.Start(prefix, suffix); err != nil {
+		utils.LogError("Failed to write YAML header", err)
+		return
+	}
+
+	// Process files
+	for req := range writeCh {
+		if err := writer.WriteFile(req); err != nil {
+			utils.LogError("Failed to write YAML file", err)
+		}
+	}
+
+	// Close writer
+	if err := writer.Close(); err != nil {
+		utils.LogError("Failed to write YAML end", err)
+	}
+}
diff --git a/go.mod b/go.mod
index dec5501..d83419a 100644
--- a/go.mod
+++ b/go.mod
@@ -3,7 +3,9 @@ module github.com/ivuorinen/gibidify
 go 1.24.1
 
 require (
+	github.com/fatih/color v1.18.0
 	github.com/sabhiram/go-gitignore v0.0.0-20210923224102-525f6e181f06
+	github.com/schollz/progressbar/v3 v3.18.0
 	github.com/sirupsen/logrus v1.9.3
 	github.com/spf13/viper v1.20.0
 	gopkg.in/yaml.v3 v3.0.1
@@ -12,7 +14,11 @@ require (
 require (
 	github.com/fsnotify/fsnotify v1.8.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/mattn/go-colorable v0.1.13 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/mitchellh/colorstring v0.0.0-20190213212951-d06e56a500db // indirect
 	github.com/pelletier/go-toml/v2 v2.2.3 // indirect
+	github.com/rivo/uniseg v0.4.7 // indirect
 	github.com/sagikazarmark/locafero v0.8.0 // indirect
 	github.com/sourcegraph/conc v0.3.0 // indirect
 	github.com/spf13/afero v1.14.0 // indirect
@@ -21,5 +27,6 @@ require (
 	github.com/subosito/gotenv v1.6.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
 	golang.org/x/sys v0.31.0 // indirect
+	golang.org/x/term v0.28.0 // indirect
 	golang.org/x/text v0.23.0 // indirect
 )
diff --git a/go.sum b/go.sum
index 7ce23c5..e8a1c14 100644
--- a/go.sum
+++ b/go.sum
@@ -1,6 +1,10 @@
+github.com/chengxilo/virtualterm v1.0.4 h1:Z6IpERbRVlfB8WkOmtbHiDbBANU7cimRIof7mk9/PwM=
+github.com/chengxilo/virtualterm v1.0.4/go.mod h1:DyxxBZz/x1iqJjFxTFcr6/x+jSpqN0iwWCOK1q10rlY=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/fatih/color v1.18.0 h1:S8gINlzdQ840/4pfAwic/ZE0djQEH3wM94VfqLTZcOM=
+github.com/fatih/color v1.18.0/go.mod h1:4FelSpRwEGDpQ12mAdzqdOukCy4u8WUtOY6lkT/6HfU=
 github.com/frankban/quicktest v1.14.6 h1:7Xjx+VpznH+oBnejlPUj8oUpdxnVs4f8XU8WnHkI4W8=
 github.com/frankban/quicktest v1.14.6/go.mod h1:4ptaffx2x8+WTWXmUCuVU6aPUX1/Mz7zb5vbUoiM6w0=
 github.com/fsnotify/fsnotify v1.8.0 h1:dAwr6QBTBZIkG8roQaJjGof0pp0EeF+tNV7YBP3F/8M=
@@ -13,16 +17,29 @@ github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
+github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxecdEvA=
+github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
+github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=
+github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
+github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
+github.com/mattn/go-runewidth v0.0.16 h1:E5ScNMtiwvlvB5paMFdw9p4kSQzbXFikJ5SQO6TULQc=
+github.com/mattn/go-runewidth v0.0.16/go.mod h1:Jdepj2loyihRzMpdS35Xk/zdY8IAYHsh153qUoGf23w=
+github.com/mitchellh/colorstring v0.0.0-20190213212951-d06e56a500db h1:62I3jR2EmQ4l5rM/4FEfDWcRD+abF5XlKShorW5LRoQ=
+github.com/mitchellh/colorstring v0.0.0-20190213212951-d06e56a500db/go.mod h1:l0dey0ia/Uv7NcFFVbCLtqEBQbrT4OCwCSKTEv6enCw=
 github.com/pelletier/go-toml/v2 v2.2.3 h1:YmeHyLY8mFWbdkNWwpr+qIL2bEqT0o95WSdkNHvL12M=
 github.com/pelletier/go-toml/v2 v2.2.3/go.mod h1:MfCQTFTvCcUyyvvwm1+G6H/jORL20Xlb6rzQu9GuUkc=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rivo/uniseg v0.4.7 h1:WUdvkW8uEhrYfLC4ZzdpI2ztxP1I582+49Oc5Mq64VQ=
+github.com/rivo/uniseg v0.4.7/go.mod h1:FN3SvrM+Zdj16jyLfmOkMNblXMcoc8DfTHruCPUcx88=
 github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/sabhiram/go-gitignore v0.0.0-20210923224102-525f6e181f06 h1:OkMGxebDjyw0ULyrTYWeN0UNCCkmCWfjPnIA2W6oviI=
 github.com/sabhiram/go-gitignore v0.0.0-20210923224102-525f6e181f06/go.mod h1:+ePHsJ1keEjQtpvf9HHw0f4ZeJ0TLRsxhunSI2hYJSs=
 github.com/sagikazarmark/locafero v0.8.0 h1:mXaMVw7IqxNBxfv3LdWt9MDmcWDQ1fagDH918lOdVaQ=
 github.com/sagikazarmark/locafero v0.8.0/go.mod h1:UBUyz37V+EdMS3hDF3QWIiVr/2dPrx49OMO0Bn0hJqk=
+github.com/schollz/progressbar/v3 v3.18.0 h1:uXdoHABRFmNIjUfte/Ex7WtuyVslrw2wVPQmCN62HpA=
+github.com/schollz/progressbar/v3 v3.18.0/go.mod h1:IsO3lpbaGuzh8zIMzgY3+J8l4C8GjO0Y9S69eFvNsec=
 github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
 github.com/sirupsen/logrus v1.9.3/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
 github.com/sourcegraph/conc v0.3.0 h1:OQTbbt6P72L20UqAkXXuLOj79LfEanQ+YQFNpLA9ySo=
@@ -45,8 +62,12 @@ github.com/subosito/gotenv v1.6.0/go.mod h1:Dk4QP5c2W3ibzajGcXpNraDfq2IrhjMIvMSW
 go.uber.org/multierr v1.11.0 h1:blXXJkSxSSfBVBlC76pxqeO+LN3aDfLQo+309xJstO0=
 go.uber.org/multierr v1.11.0/go.mod h1:20+QtiLqy0Nd6FdQB9TLXag12DsQkrbs3htMFfDN80Y=
 golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.31.0 h1:ioabZlmFYtWhL+TRYpcnNlLwhyxaM9kWTDEmfnprqik=
 golang.org/x/sys v0.31.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+golang.org/x/term v0.28.0 h1:/Ts8HFuMR2E6IP/jlo7QVLZHggjKQbhu/7H0LJFr3Gg=
+golang.org/x/term v0.28.0/go.mod h1:Sw/lC2IAUZ92udQNf3WodGtn4k/XoLyZoh8v/8uiwek=
 golang.org/x/text v0.23.0 h1:D71I7dUrlY+VX0gQShAThNGHFxZ13dGLBHQLVl1mJlY=
 golang.org/x/text v0.23.0/go.mod h1:/BLNzu4aZCJ1+kcD0DNRotWKage4q2rGVAg4o22unh4=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
diff --git a/main.go b/main.go
index 6510a7c..c768396 100644
--- a/main.go
+++ b/main.go
@@ -4,152 +4,46 @@ package main
 
 import (
 	"context"
-	"flag"
-	"fmt"
 	"os"
-	"path/filepath"
-	"runtime"
-	"sync"
 
-	"github.com/ivuorinen/gibidify/config"
-	"github.com/ivuorinen/gibidify/fileproc"
 	"github.com/sirupsen/logrus"
-)
 
-var (
-	sourceDir   string
-	destination string
-	prefix      string
-	suffix      string
-	concurrency int
-	format      string
+	"github.com/ivuorinen/gibidify/cli"
+	"github.com/ivuorinen/gibidify/config"
 )
 
-func init() {
-	flag.StringVar(&sourceDir, "source", "", "Source directory to scan recursively")
-	flag.StringVar(&destination, "destination", "", "Output file to write aggregated code")
-	flag.StringVar(&prefix, "prefix", "", "Text to add at the beginning of the output file")
-	flag.StringVar(&suffix, "suffix", "", "Text to add at the end of the output file")
-	flag.StringVar(&format, "format", "markdown", "Output format (json, markdown, yaml)")
-	flag.IntVar(&concurrency, "concurrency", runtime.NumCPU(), "Number of concurrent workers (default: number of CPU cores)")
-}
-
 func main() {
+	// Initialize UI for error handling
+	ui := cli.NewUIManager()
+	errorFormatter := cli.NewErrorFormatter(ui)
+
 	// In production, use a background context.
 	if err := run(context.Background()); err != nil {
-		fmt.Println("Error:", err)
-		os.Exit(1)
+		// Handle errors with better formatting and suggestions
+		if cli.IsUserError(err) {
+			errorFormatter.FormatError(err)
+			os.Exit(1)
+		} else {
+			// System errors still go to logrus for debugging
+			logrus.Errorf("System error: %v", err)
+			ui.PrintError("An unexpected error occurred. Please check the logs.")
+			os.Exit(2)
+		}
 	}
 }
 
 // Run executes the main logic of the CLI application using the provided context.
 func run(ctx context.Context) error {
-	flag.Parse()
-
-	if err := validateFlags(); err != nil {
-		return err
-	}
-
-	if err := setDestination(); err != nil {
+	// Parse CLI flags
+	flags, err := cli.ParseFlags()
+	if err != nil {
 		return err
 	}
 
+	// Load configuration
 	config.LoadConfig()
 
-	logrus.Infof(
-		"Starting gibidify. Format: %s, Source: %s, Destination: %s, Workers: %d",
-		format,
-		sourceDir,
-		destination,
-		concurrency,
-	)
-
-	files, err := fileproc.CollectFiles(sourceDir)
-	if err != nil {
-		return fmt.Errorf("error collecting files: %w", err)
-	}
-	logrus.Infof("Found %d files to process", len(files))
-
-	outFile, err := os.Create(destination)
-	if err != nil {
-		return fmt.Errorf("failed to create output file %s: %w", destination, err)
-	}
-	defer func(outFile *os.File) {
-		if err := outFile.Close(); err != nil {
-			logrus.Errorf("Error closing output file: %v", err)
-		}
-	}(outFile)
-
-	fileCh := make(chan string)
-	writeCh := make(chan fileproc.WriteRequest)
-	writerDone := make(chan struct{})
-
-	go fileproc.StartWriter(outFile, writeCh, writerDone, format, prefix, suffix)
-
-	var wg sync.WaitGroup
-
-	startWorkers(ctx, &wg, fileCh, writeCh)
-
-	for _, fp := range files {
-		select {
-		case <-ctx.Done():
-			close(fileCh)
-			return ctx.Err()
-		case fileCh <- fp:
-		}
-	}
-	close(fileCh)
-
-	wg.Wait()
-	close(writeCh)
-	<-writerDone
-
-	logrus.Infof("Processing completed. Output saved to %s", destination)
-	return nil
-}
-func validateFlags() error {
-	if sourceDir == "" {
-		return fmt.Errorf("usage: gibidify -source <source_directory> [--destination <output_file>] [--format=json|yaml|markdown] ")
-	}
-	return nil
-}
-
-func setDestination() error {
-	if destination == "" {
-		absRoot, err := filepath.Abs(sourceDir)
-		if err != nil {
-			return fmt.Errorf("failed to get absolute path for %s: %w", sourceDir, err)
-		}
-		baseName := filepath.Base(absRoot)
-		if baseName == "." || baseName == "" {
-			baseName = "output"
-		}
-		destination = baseName + "." + format
-	}
-	return nil
-}
-
-func startWorkers(ctx context.Context, wg *sync.WaitGroup, fileCh chan string, writeCh chan fileproc.WriteRequest) {
-	for i := 0; i < concurrency; i++ {
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			for {
-				select {
-				case <-ctx.Done():
-					return
-				case filePath, ok := <-fileCh:
-					if !ok {
-						return
-					}
-					absRoot, err := filepath.Abs(sourceDir)
-					if err != nil {
-						logrus.Errorf("Failed to get absolute path for %s: %v", sourceDir, err)
-						return
-					}
-					fileproc.ProcessFile(filePath, writeCh, absRoot)
-				}
-			}
-		}()
-	}
+	// Create and run processor
+	processor := cli.NewProcessor(flags)
+	return processor.Process(ctx)
 }
diff --git a/main_test.go b/main_test.go
index a7372cf..ab89aac 100644
--- a/main_test.go
+++ b/main_test.go
@@ -4,139 +4,103 @@ import (
 	"context"
 	"fmt"
 	"os"
-	"path/filepath"
-	"strings"
 	"testing"
 	"time"
+
+	"github.com/ivuorinen/gibidify/testutil"
+)
+
+const (
+	testFileCount = 1000
 )
 
 // TestIntegrationFullCLI simulates a full run of the CLI application using adaptive concurrency.
 func TestIntegrationFullCLI(t *testing.T) {
-	// Create a temporary source directory and populate it with test files.
-	srcDir, err := os.MkdirTemp("", "gibidify_src")
-	if err != nil {
-		t.Fatalf("Failed to create temp source directory: %v", err)
-	}
-	defer func() {
-		if err := os.RemoveAll(srcDir); err != nil {
-			t.Fatalf("cleanup failed: %v", err)
-		}
-	}()
-
-	// Create two test files.
-	file1 := filepath.Join(srcDir, "file1.txt")
-	if err := os.WriteFile(file1, []byte("Hello World"), 0644); err != nil {
-		t.Fatalf("Failed to write file1: %v", err)
-	}
-	file2 := filepath.Join(srcDir, "file2.go")
-	if err := os.WriteFile(file2, []byte("package main\nfunc main() {}"), 0644); err != nil {
-		t.Fatalf("Failed to write file2: %v", err)
-	}
-
-	// Create a temporary output file.
-	outFile, err := os.CreateTemp("", "gibidify_output.txt")
-	if err != nil {
-		t.Fatalf("Failed to create temp output file: %v", err)
-	}
-	outFilePath := outFile.Name()
-	if err := outFile.Close(); err != nil {
-		t.Fatalf("close temp file: %v", err)
-	}
-	defer func() {
-		if err := os.Remove(outFilePath); err != nil {
-			t.Fatalf("cleanup output file: %v", err)
-		}
-	}()
-
-	// Set up CLI arguments.
-	os.Args = []string{
-		"gibidify",
-		"-source", srcDir,
-		"-destination", outFilePath,
-		"-prefix", "PREFIX",
-		"-suffix", "SUFFIX",
-		"-concurrency", "2", // For testing, set concurrency to 2.
-	}
+	srcDir := setupTestFiles(t)
+	outFilePath := setupOutputFile(t)
+	setupCLIArgs(srcDir, outFilePath)
 
 	// Run the application with a background context.
-	ctx := context.Background()
-	if err := run(ctx); err != nil {
-		t.Fatalf("Run failed: %v", err)
+	ctx := t.Context()
+	if runErr := run(ctx); runErr != nil {
+		t.Fatalf("Run failed: %v", runErr)
 	}
 
-	// Verify the output file contains the expected prefix, file contents, and suffix.
+	verifyOutput(t, outFilePath)
+}
+
+// setupTestFiles creates test files and returns the source directory.
+func setupTestFiles(t *testing.T) string {
+	t.Helper()
+	srcDir := t.TempDir()
+
+	// Create two test files.
+	testutil.CreateTestFiles(t, srcDir, []testutil.FileSpec{
+		{Name: "file1.txt", Content: "Hello World"},
+		{Name: "file2.go", Content: "package main\nfunc main() {}"},
+	})
+
+	return srcDir
+}
+
+// setupOutputFile creates a temporary output file and returns its path.
+func setupOutputFile(t *testing.T) string {
+	t.Helper()
+	outFile, outFilePath := testutil.CreateTempOutputFile(t, "gibidify_output.txt")
+	testutil.CloseFile(t, outFile)
+
+	return outFilePath
+}
+
+// setupCLIArgs configures the CLI arguments for testing.
+func setupCLIArgs(srcDir, outFilePath string) {
+	testutil.SetupCLIArgs(srcDir, outFilePath, "PREFIX", "SUFFIX", 2)
+}
+
+// verifyOutput checks that the output file contains expected content.
+func verifyOutput(t *testing.T, outFilePath string) {
+	t.Helper()
 	data, err := os.ReadFile(outFilePath)
 	if err != nil {
 		t.Fatalf("Failed to read output file: %v", err)
 	}
 	output := string(data)
-	if !strings.Contains(output, "PREFIX") {
-		t.Error("Output missing prefix")
-	}
-	if !strings.Contains(output, "Hello World") {
-		t.Error("Output missing content from file1.txt")
-	}
-	if !strings.Contains(output, "SUFFIX") {
-		t.Error("Output missing suffix")
-	}
+	testutil.VerifyContentContains(t, output, []string{"PREFIX", "Hello World", "SUFFIX"})
 }
 
 // TestIntegrationCancellation verifies that the application correctly cancels processing when the context times out.
 func TestIntegrationCancellation(t *testing.T) {
 	// Create a temporary source directory with many files to simulate a long-running process.
-	srcDir, err := os.MkdirTemp("", "gibidify_src_long")
-	if err != nil {
-		t.Fatalf("Failed to create temp source directory: %v", err)
-	}
-	defer func() {
-		if err := os.RemoveAll(srcDir); err != nil {
-			t.Fatalf("cleanup failed: %v", err)
-		}
-	}()
+	srcDir := t.TempDir()
 
 	// Create a large number of small files.
-	for i := 0; i < 1000; i++ {
-		filePath := filepath.Join(srcDir, fmt.Sprintf("file%d.txt", i))
-		if err := os.WriteFile(filePath, []byte("Content"), 0644); err != nil {
-			t.Fatalf("Failed to write %s: %v", filePath, err)
-		}
+	for i := range testFileCount {
+		fileName := fmt.Sprintf("file%d.txt", i)
+		testutil.CreateTestFile(t, srcDir, fileName, []byte("Content"))
 	}
 
 	// Create a temporary output file.
-	outFile, err := os.CreateTemp("", "gibidify_output.txt")
-	if err != nil {
-		t.Fatalf("Failed to create temp output file: %v", err)
-	}
-	outFilePath := outFile.Name()
-	if err := outFile.Close(); err != nil {
-		t.Fatalf("close temp file: %v", err)
-	}
+	outFile, outFilePath := testutil.CreateTempOutputFile(t, "gibidify_output.txt")
+	testutil.CloseFile(t, outFile)
 	defer func() {
-		if err := os.Remove(outFilePath); err != nil {
-			t.Fatalf("cleanup output file: %v", err)
+		if removeErr := os.Remove(outFilePath); removeErr != nil {
+			t.Fatalf("cleanup output file: %v", removeErr)
 		}
 	}()
 
 	// Set up CLI arguments.
-	os.Args = []string{
-		"gibidify",
-		"-source", srcDir,
-		"-destination", outFilePath,
-		"-prefix", "PREFIX",
-		"-suffix", "SUFFIX",
-		"-concurrency", "2",
-	}
+	testutil.SetupCLIArgs(srcDir, outFilePath, "PREFIX", "SUFFIX", 2)
 
 	// Create a context with a very short timeout to force cancellation.
 	ctx, cancel := context.WithTimeout(
-		context.Background(),
-		10*time.Millisecond,
+		t.Context(),
+		1*time.Millisecond,
 	)
 	defer cancel()
 
 	// Run the application; we expect an error due to cancellation.
-	err = run(ctx)
-	if err == nil {
+	runErr := run(ctx)
+	if runErr == nil {
 		t.Error("Expected Run to fail due to cancellation, but it succeeded")
 	}
 }
diff --git a/testutil/testutil.go b/testutil/testutil.go
new file mode 100644
index 0000000..ecc43c4
--- /dev/null
+++ b/testutil/testutil.go
@@ -0,0 +1,117 @@
+// Package testutil provides common testing utilities and helper functions.
+package testutil
+
+import (
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/spf13/viper"
+
+	"github.com/ivuorinen/gibidify/config"
+)
+
+const (
+	// FilePermission is the default file permission for test files.
+	FilePermission = 0o644
+	// DirPermission is the default directory permission for test directories.
+	DirPermission = 0o755
+)
+
+// CreateTestFile creates a test file with the given content and returns its path.
+func CreateTestFile(t *testing.T, dir, filename string, content []byte) string {
+	t.Helper()
+	filePath := filepath.Join(dir, filename)
+	if err := os.WriteFile(filePath, content, FilePermission); err != nil {
+		t.Fatalf("Failed to write file %s: %v", filePath, err)
+	}
+	return filePath
+}
+
+// CreateTempOutputFile creates a temporary output file and returns the file handle and path.
+func CreateTempOutputFile(t *testing.T, pattern string) (file *os.File, path string) {
+	t.Helper()
+	outFile, err := os.CreateTemp(t.TempDir(), pattern)
+	if err != nil {
+		t.Fatalf("Failed to create temp output file: %v", err)
+	}
+	path = outFile.Name()
+	return outFile, path
+}
+
+// CreateTestDirectory creates a test directory and returns its path.
+func CreateTestDirectory(t *testing.T, parent, name string) string {
+	t.Helper()
+	dirPath := filepath.Join(parent, name)
+	if err := os.Mkdir(dirPath, DirPermission); err != nil {
+		t.Fatalf("Failed to create directory %s: %v", dirPath, err)
+	}
+	return dirPath
+}
+
+// FileSpec represents a file specification for creating test files.
+type FileSpec struct {
+	Name    string
+	Content string
+}
+
+// CreateTestFiles creates multiple test files from specifications.
+func CreateTestFiles(t *testing.T, rootDir string, fileSpecs []FileSpec) []string {
+	t.Helper()
+	createdFiles := make([]string, 0, len(fileSpecs))
+	for _, spec := range fileSpecs {
+		filePath := CreateTestFile(t, rootDir, spec.Name, []byte(spec.Content))
+		createdFiles = append(createdFiles, filePath)
+	}
+	return createdFiles
+}
+
+// ResetViperConfig resets Viper configuration and optionally sets a config path.
+func ResetViperConfig(t *testing.T, configPath string) {
+	t.Helper()
+	viper.Reset()
+	if configPath != "" {
+		viper.AddConfigPath(configPath)
+	}
+	config.LoadConfig()
+}
+
+// SetupCLIArgs configures os.Args for CLI testing.
+func SetupCLIArgs(srcDir, outFilePath, prefix, suffix string, concurrency int) {
+	os.Args = []string{
+		"gibidify",
+		"-source", srcDir,
+		"-destination", outFilePath,
+		"-prefix", prefix,
+		"-suffix", suffix,
+		"-concurrency", strconv.Itoa(concurrency),
+	}
+}
+
+// VerifyContentContains checks that content contains all expected substrings.
+func VerifyContentContains(t *testing.T, content string, expectedSubstrings []string) {
+	t.Helper()
+	for _, expected := range expectedSubstrings {
+		if !strings.Contains(content, expected) {
+			t.Errorf("Content missing expected substring: %s", expected)
+		}
+	}
+}
+
+// MustSucceed fails the test if the error is not nil.
+func MustSucceed(t *testing.T, err error, operation string) {
+	t.Helper()
+	if err != nil {
+		t.Fatalf("Operation %s failed: %v", operation, err)
+	}
+}
+
+// CloseFile closes a file and reports errors to the test.
+func CloseFile(t *testing.T, file *os.File) {
+	t.Helper()
+	if err := file.Close(); err != nil {
+		t.Errorf("Failed to close file: %v", err)
+	}
+}
diff --git a/testutil/testutil_test.go b/testutil/testutil_test.go
new file mode 100644
index 0000000..b2eaf30
--- /dev/null
+++ b/testutil/testutil_test.go
@@ -0,0 +1,591 @@
+package testutil
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/spf13/viper"
+)
+
+func TestCreateTestFile(t *testing.T) {
+	tests := []struct {
+		name     string
+		dir      string
+		filename string
+		content  []byte
+		wantErr  bool
+	}{
+		{
+			name:     "create simple test file",
+			filename: "test.txt",
+			content:  []byte("hello world"),
+			wantErr:  false,
+		},
+		{
+			name:     "create file with empty content",
+			filename: "empty.txt",
+			content:  []byte{},
+			wantErr:  false,
+		},
+		{
+			name:     "create file with binary content",
+			filename: "binary.bin",
+			content:  []byte{0x00, 0xFF, 0x42},
+			wantErr:  false,
+		},
+		{
+			name:     "create file with subdirectory",
+			filename: "subdir/test.txt",
+			content:  []byte("nested file"),
+			wantErr:  false,
+		},
+		{
+			name:     "create file with special characters",
+			filename: "special-file_123.go",
+			content:  []byte("package main"),
+			wantErr:  false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Use a temporary directory for each test
+			tempDir := t.TempDir()
+			if tt.dir == "" {
+				tt.dir = tempDir
+			}
+
+			// Create subdirectory if needed
+			if strings.Contains(tt.filename, "/") {
+				subdir := filepath.Join(tt.dir, filepath.Dir(tt.filename))
+				if err := os.MkdirAll(subdir, DirPermission); err != nil {
+					t.Fatalf("Failed to create subdirectory: %v", err)
+				}
+			}
+
+			// Test CreateTestFile
+			filePath := CreateTestFile(t, tt.dir, tt.filename, tt.content)
+
+			// Verify file exists
+			info, err := os.Stat(filePath)
+			if err != nil {
+				t.Fatalf("Created file does not exist: %v", err)
+			}
+
+			// Verify it's a regular file
+			if !info.Mode().IsRegular() {
+				t.Errorf("Created path is not a regular file")
+			}
+
+			// Verify permissions
+			if info.Mode().Perm() != FilePermission {
+				t.Errorf("File permissions = %v, want %v", info.Mode().Perm(), FilePermission)
+			}
+
+			// Verify content
+			readContent, err := os.ReadFile(filePath)
+			if err != nil {
+				t.Fatalf("Failed to read created file: %v", err)
+			}
+			if string(readContent) != string(tt.content) {
+				t.Errorf("File content = %q, want %q", readContent, tt.content)
+			}
+		})
+	}
+}
+
+func TestCreateTempOutputFile(t *testing.T) {
+	tests := []struct {
+		name    string
+		pattern string
+	}{
+		{
+			name:    "simple pattern",
+			pattern: "output-*.txt",
+		},
+		{
+			name:    "pattern with prefix only",
+			pattern: "test-",
+		},
+		{
+			name:    "pattern with suffix only",
+			pattern: "*.json",
+		},
+		{
+			name:    "empty pattern",
+			pattern: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			file, path := CreateTempOutputFile(t, tt.pattern)
+			defer CloseFile(t, file)
+
+			// Verify file exists
+			info, err := os.Stat(path)
+			if err != nil {
+				t.Fatalf("Temp file does not exist: %v", err)
+			}
+
+			// Verify it's a regular file
+			if !info.Mode().IsRegular() {
+				t.Errorf("Created path is not a regular file")
+			}
+
+			// Verify we can write to it
+			testContent := []byte("test content")
+			if _, err := file.Write(testContent); err != nil {
+				t.Errorf("Failed to write to temp file: %v", err)
+			}
+
+			// Verify the path is in a temp directory (any temp directory)
+			if !strings.Contains(path, os.TempDir()) {
+				t.Errorf("Temp file not in temp directory: %s", path)
+			}
+		})
+	}
+}
+
+func TestCreateTestDirectory(t *testing.T) {
+	tests := []struct {
+		name   string
+		parent string
+		dir    string
+	}{
+		{
+			name: "simple directory",
+			dir:  "testdir",
+		},
+		{
+			name: "directory with special characters",
+			dir:  "test-dir_123",
+		},
+		{
+			name: "nested directory name",
+			dir:  "nested/dir",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tempDir := t.TempDir()
+			if tt.parent == "" {
+				tt.parent = tempDir
+			}
+
+			// For nested directories, create parent first
+			if strings.Contains(tt.dir, "/") {
+				parentPath := filepath.Join(tt.parent, filepath.Dir(tt.dir))
+				if err := os.MkdirAll(parentPath, DirPermission); err != nil {
+					t.Fatalf("Failed to create parent directory: %v", err)
+				}
+				tt.dir = filepath.Base(tt.dir)
+				tt.parent = parentPath
+			}
+
+			dirPath := CreateTestDirectory(t, tt.parent, tt.dir)
+
+			// Verify directory exists
+			info, err := os.Stat(dirPath)
+			if err != nil {
+				t.Fatalf("Created directory does not exist: %v", err)
+			}
+
+			// Verify it's a directory
+			if !info.IsDir() {
+				t.Errorf("Created path is not a directory")
+			}
+
+			// Verify permissions
+			if info.Mode().Perm() != DirPermission {
+				t.Errorf("Directory permissions = %v, want %v", info.Mode().Perm(), DirPermission)
+			}
+
+			// Verify we can create files in it
+			testFile := filepath.Join(dirPath, "test.txt")
+			if err := os.WriteFile(testFile, []byte("test"), FilePermission); err != nil {
+				t.Errorf("Cannot create file in directory: %v", err)
+			}
+		})
+	}
+}
+
+func TestCreateTestFiles(t *testing.T) {
+	tests := []struct {
+		name      string
+		fileSpecs []FileSpec
+		wantCount int
+	}{
+		{
+			name: "create multiple files",
+			fileSpecs: []FileSpec{
+				{Name: "file1.txt", Content: "content1"},
+				{Name: "file2.go", Content: "package main"},
+				{Name: "file3.json", Content: `{"key": "value"}`},
+			},
+			wantCount: 3,
+		},
+		{
+			name: "create files with subdirectories",
+			fileSpecs: []FileSpec{
+				{Name: "src/main.go", Content: "package main"},
+				{Name: "test/test.go", Content: "package test"},
+			},
+			wantCount: 2,
+		},
+		{
+			name:      "empty file specs",
+			fileSpecs: []FileSpec{},
+			wantCount: 0,
+		},
+		{
+			name: "files with empty content",
+			fileSpecs: []FileSpec{
+				{Name: "empty1.txt", Content: ""},
+				{Name: "empty2.txt", Content: ""},
+			},
+			wantCount: 2,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			rootDir := t.TempDir()
+
+			// Create necessary subdirectories
+			for _, spec := range tt.fileSpecs {
+				if strings.Contains(spec.Name, "/") {
+					subdir := filepath.Join(rootDir, filepath.Dir(spec.Name))
+					if err := os.MkdirAll(subdir, DirPermission); err != nil {
+						t.Fatalf("Failed to create subdirectory: %v", err)
+					}
+				}
+			}
+
+			createdFiles := CreateTestFiles(t, rootDir, tt.fileSpecs)
+
+			// Verify count
+			if len(createdFiles) != tt.wantCount {
+				t.Errorf("Created %d files, want %d", len(createdFiles), tt.wantCount)
+			}
+
+			// Verify each file
+			for i, filePath := range createdFiles {
+				content, err := os.ReadFile(filePath)
+				if err != nil {
+					t.Errorf("Failed to read file %s: %v", filePath, err)
+					continue
+				}
+				if string(content) != tt.fileSpecs[i].Content {
+					t.Errorf("File %s content = %q, want %q", filePath, content, tt.fileSpecs[i].Content)
+				}
+			}
+		})
+	}
+}
+
+func TestResetViperConfig(t *testing.T) {
+	tests := []struct {
+		name       string
+		configPath string
+		preSetup   func()
+		verify     func(t *testing.T)
+	}{
+		{
+			name:       "reset with empty config path",
+			configPath: "",
+			preSetup: func() {
+				viper.Set("test.key", "value")
+			},
+			verify: func(t *testing.T) {
+				if viper.IsSet("test.key") {
+					t.Error("Viper config not reset properly")
+				}
+			},
+		},
+		{
+			name:       "reset with config path",
+			configPath: t.TempDir(),
+			preSetup: func() {
+				viper.Set("test.key", "value")
+			},
+			verify: func(t *testing.T) {
+				if viper.IsSet("test.key") {
+					t.Error("Viper config not reset properly")
+				}
+				// Verify config path was added
+				paths := viper.ConfigFileUsed()
+				if paths == "" {
+					// This is expected as no config file exists
+					return
+				}
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tt.preSetup()
+			ResetViperConfig(t, tt.configPath)
+			tt.verify(t)
+		})
+	}
+}
+
+func TestSetupCLIArgs(t *testing.T) {
+	// Save original args
+	originalArgs := os.Args
+	defer func() {
+		os.Args = originalArgs
+	}()
+
+	tests := []struct {
+		name        string
+		srcDir      string
+		outFile     string
+		prefix      string
+		suffix      string
+		concurrency int
+		wantLen     int
+	}{
+		{
+			name:        "basic CLI args",
+			srcDir:      "/src",
+			outFile:     "/out.txt",
+			prefix:      "PREFIX",
+			suffix:      "SUFFIX",
+			concurrency: 4,
+			wantLen:     11,
+		},
+		{
+			name:        "empty strings",
+			srcDir:      "",
+			outFile:     "",
+			prefix:      "",
+			suffix:      "",
+			concurrency: 1,
+			wantLen:     11,
+		},
+		{
+			name:        "special characters in args",
+			srcDir:      "/path with spaces/src",
+			outFile:     "/path/to/output file.txt",
+			prefix:      "Prefix with\nnewline",
+			suffix:      "Suffix with\ttab",
+			concurrency: 8,
+			wantLen:     11,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			SetupCLIArgs(tt.srcDir, tt.outFile, tt.prefix, tt.suffix, tt.concurrency)
+
+			if len(os.Args) != tt.wantLen {
+				t.Errorf("os.Args length = %d, want %d", len(os.Args), tt.wantLen)
+			}
+
+			// Verify specific args
+			if os.Args[0] != "gibidify" {
+				t.Errorf("Program name = %s, want gibidify", os.Args[0])
+			}
+			if os.Args[2] != tt.srcDir {
+				t.Errorf("Source dir = %s, want %s", os.Args[2], tt.srcDir)
+			}
+			if os.Args[4] != tt.outFile {
+				t.Errorf("Output file = %s, want %s", os.Args[4], tt.outFile)
+			}
+			if os.Args[6] != tt.prefix {
+				t.Errorf("Prefix = %s, want %s", os.Args[6], tt.prefix)
+			}
+			if os.Args[8] != tt.suffix {
+				t.Errorf("Suffix = %s, want %s", os.Args[8], tt.suffix)
+			}
+			if os.Args[10] != string(rune(tt.concurrency+'0')) {
+				t.Errorf("Concurrency = %s, want %d", os.Args[10], tt.concurrency)
+			}
+		})
+	}
+}
+
+func TestVerifyContentContains(t *testing.T) {
+	// Test successful verification
+	t.Run("all substrings present", func(t *testing.T) {
+		content := "This is a test file with multiple lines"
+		VerifyContentContains(t, content, []string{"test file", "multiple lines"})
+		// If we get here, the test passed
+	})
+
+	// Test empty expected substrings
+	t.Run("empty expected substrings", func(t *testing.T) {
+		content := "Any content"
+		VerifyContentContains(t, content, []string{})
+		// Should pass with no expected strings
+	})
+
+	// For failure cases, we'll test indirectly by verifying behavior
+	t.Run("verify error reporting", func(t *testing.T) {
+		// We can't easily test the failure case directly since it calls t.Errorf
+		// But we can at least verify the function doesn't panic
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("VerifyContentContains panicked: %v", r)
+			}
+		}()
+
+		// This would normally fail but we're just checking it doesn't panic
+		content := "test"
+		expected := []string{"not found"}
+		// Create a sub-test that we expect to fail
+		t.Run("expected_failure", func(t *testing.T) {
+			t.Skip("Skipping actual failure test")
+			VerifyContentContains(t, content, expected)
+		})
+	})
+}
+
+func TestMustSucceed(t *testing.T) {
+	// Test with nil error (should succeed)
+	t.Run("nil error", func(t *testing.T) {
+		MustSucceed(t, nil, "successful operation")
+		// If we get here, the test passed
+	})
+
+	// Test error behavior without causing test failure
+	t.Run("verify error handling", func(t *testing.T) {
+		// We can't test the failure case directly since it calls t.Fatalf
+		// But we can verify the function exists and is callable
+		defer func() {
+			if r := recover(); r != nil {
+				t.Errorf("MustSucceed panicked: %v", r)
+			}
+		}()
+
+		// Create a sub-test that we expect to fail
+		t.Run("expected_failure", func(t *testing.T) {
+			t.Skip("Skipping actual failure test")
+			MustSucceed(t, errors.New("test error"), "failed operation")
+		})
+	})
+}
+
+func TestCloseFile(t *testing.T) {
+	// Test closing a normal file
+	t.Run("close normal file", func(t *testing.T) {
+		file, err := os.CreateTemp(t.TempDir(), "test")
+		if err != nil {
+			t.Fatalf("Failed to create test file: %v", err)
+		}
+
+		CloseFile(t, file)
+
+		// Verify file is closed by trying to write to it
+		_, writeErr := file.Write([]byte("test"))
+		if writeErr == nil {
+			t.Error("Expected write to fail on closed file")
+		}
+	})
+
+	// Test that CloseFile doesn't panic on already closed files
+	// Note: We can't easily test the error case without causing test failure
+	// since CloseFile calls t.Errorf, which is the expected behavior
+	t.Run("verify CloseFile function exists and is callable", func(t *testing.T) {
+		// This test just verifies the function signature and basic functionality
+		// The error case is tested in integration tests where failures are expected
+		file, err := os.CreateTemp(t.TempDir(), "test")
+		if err != nil {
+			t.Fatalf("Failed to create test file: %v", err)
+		}
+
+		// Test normal case - file should close successfully
+		CloseFile(t, file)
+
+		// Verify file is closed
+		_, writeErr := file.Write([]byte("test"))
+		if writeErr == nil {
+			t.Error("Expected write to fail on closed file")
+		}
+	})
+}
+
+// Test thread safety of functions that might be called concurrently
+func TestConcurrentOperations(t *testing.T) {
+	tempDir := t.TempDir()
+	done := make(chan bool)
+
+	// Test concurrent file creation
+	for i := 0; i < 5; i++ {
+		go func(n int) {
+			CreateTestFile(t, tempDir, string(rune('a'+n))+".txt", []byte("content"))
+			done <- true
+		}(i)
+	}
+
+	// Test concurrent directory creation
+	for i := 0; i < 5; i++ {
+		go func(n int) {
+			CreateTestDirectory(t, tempDir, "dir"+string(rune('0'+n)))
+			done <- true
+		}(i)
+	}
+
+	// Wait for all goroutines
+	for i := 0; i < 10; i++ {
+		<-done
+	}
+}
+
+// Benchmarks
+func BenchmarkCreateTestFile(b *testing.B) {
+	tempDir := b.TempDir()
+	content := []byte("benchmark content")
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		// Use a unique filename for each iteration to avoid conflicts
+		filename := "bench" + string(rune(i%26+'a')) + ".txt"
+		filePath := filepath.Join(tempDir, filename)
+		if err := os.WriteFile(filePath, content, FilePermission); err != nil {
+			b.Fatalf("Failed to write file: %v", err)
+		}
+	}
+}
+
+func BenchmarkCreateTestFiles(b *testing.B) {
+	tempDir := b.TempDir()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		// Create specs with unique names for each iteration
+		specs := []FileSpec{
+			{Name: "file1_" + string(rune(i%26+'a')) + ".txt", Content: "content1"},
+			{Name: "file2_" + string(rune(i%26+'a')) + ".txt", Content: "content2"},
+			{Name: "file3_" + string(rune(i%26+'a')) + ".txt", Content: "content3"},
+		}
+
+		for _, spec := range specs {
+			filePath := filepath.Join(tempDir, spec.Name)
+			if err := os.WriteFile(filePath, []byte(spec.Content), FilePermission); err != nil {
+				b.Fatalf("Failed to write file: %v", err)
+			}
+		}
+	}
+}
+
+func BenchmarkVerifyContentContains(b *testing.B) {
+	content := strings.Repeat("test content with various words ", 100)
+	expected := []string{"test", "content", "various", "words"}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		// We can't use the actual function in benchmark since it needs testing.T
+		// So we'll benchmark the core logic
+		for _, exp := range expected {
+			_ = strings.Contains(content, exp)
+		}
+	}
+}
diff --git a/utils/errors.go b/utils/errors.go
new file mode 100644
index 0000000..4e74402
--- /dev/null
+++ b/utils/errors.go
@@ -0,0 +1,228 @@
+// Package utils provides common utility functions.
+package utils
+
+import (
+	"fmt"
+
+	"github.com/sirupsen/logrus"
+)
+
+// ErrorType represents the category of error.
+type ErrorType int
+
+const (
+	// ErrorTypeUnknown represents an unknown error type.
+	ErrorTypeUnknown ErrorType = iota
+	// ErrorTypeCLI represents command-line interface errors.
+	ErrorTypeCLI
+	// ErrorTypeFileSystem represents file system operation errors.
+	ErrorTypeFileSystem
+	// ErrorTypeProcessing represents file processing errors.
+	ErrorTypeProcessing
+	// ErrorTypeConfiguration represents configuration errors.
+	ErrorTypeConfiguration
+	// ErrorTypeIO represents input/output errors.
+	ErrorTypeIO
+	// ErrorTypeValidation represents validation errors.
+	ErrorTypeValidation
+)
+
+// String returns the string representation of the error type.
+func (e ErrorType) String() string {
+	switch e {
+	case ErrorTypeCLI:
+		return "CLI"
+	case ErrorTypeFileSystem:
+		return "FileSystem"
+	case ErrorTypeProcessing:
+		return "Processing"
+	case ErrorTypeConfiguration:
+		return "Configuration"
+	case ErrorTypeIO:
+		return "IO"
+	case ErrorTypeValidation:
+		return "Validation"
+	default:
+		return "Unknown"
+	}
+}
+
+// StructuredError represents a structured error with type, code, and context.
+type StructuredError struct {
+	Type     ErrorType
+	Code     string
+	Message  string
+	Cause    error
+	Context  map[string]any
+	FilePath string
+	Line     int
+}
+
+// Error implements the error interface.
+func (e *StructuredError) Error() string {
+	if e.Cause != nil {
+		return fmt.Sprintf("%s [%s]: %s: %v", e.Type, e.Code, e.Message, e.Cause)
+	}
+	return fmt.Sprintf("%s [%s]: %s", e.Type, e.Code, e.Message)
+}
+
+// Unwrap returns the underlying cause error.
+func (e *StructuredError) Unwrap() error {
+	return e.Cause
+}
+
+// WithContext adds context information to the error.
+func (e *StructuredError) WithContext(key string, value any) *StructuredError {
+	if e.Context == nil {
+		e.Context = make(map[string]any)
+	}
+	e.Context[key] = value
+	return e
+}
+
+// WithFilePath adds file path information to the error.
+func (e *StructuredError) WithFilePath(filePath string) *StructuredError {
+	e.FilePath = filePath
+	return e
+}
+
+// WithLine adds line number information to the error.
+func (e *StructuredError) WithLine(line int) *StructuredError {
+	e.Line = line
+	return e
+}
+
+// NewStructuredError creates a new structured error.
+func NewStructuredError(errorType ErrorType, code, message string) *StructuredError {
+	return &StructuredError{
+		Type:    errorType,
+		Code:    code,
+		Message: message,
+	}
+}
+
+// NewStructuredErrorf creates a new structured error with formatted message.
+func NewStructuredErrorf(errorType ErrorType, code, format string, args ...any) *StructuredError {
+	return &StructuredError{
+		Type:    errorType,
+		Code:    code,
+		Message: fmt.Sprintf(format, args...),
+	}
+}
+
+// WrapError wraps an existing error with structured error information.
+func WrapError(err error, errorType ErrorType, code, message string) *StructuredError {
+	return &StructuredError{
+		Type:    errorType,
+		Code:    code,
+		Message: message,
+		Cause:   err,
+	}
+}
+
+// WrapErrorf wraps an existing error with formatted message.
+func WrapErrorf(err error, errorType ErrorType, code, format string, args ...any) *StructuredError {
+	return &StructuredError{
+		Type:    errorType,
+		Code:    code,
+		Message: fmt.Sprintf(format, args...),
+		Cause:   err,
+	}
+}
+
+// Common error codes for each type
+const (
+	// CLI Error Codes
+	CodeCLIMissingSource = "MISSING_SOURCE"
+	CodeCLIInvalidArgs   = "INVALID_ARGS"
+
+	// FileSystem Error Codes
+	CodeFSPathResolution = "PATH_RESOLUTION"
+	CodeFSPermission     = "PERMISSION_DENIED"
+	CodeFSNotFound       = "NOT_FOUND"
+	CodeFSAccess         = "ACCESS_DENIED"
+
+	// Processing Error Codes
+	CodeProcessingFileRead   = "FILE_READ"
+	CodeProcessingCollection = "COLLECTION"
+	CodeProcessingTraversal  = "TRAVERSAL"
+	CodeProcessingEncode     = "ENCODE"
+
+	// Configuration Error Codes
+	CodeConfigValidation = "VALIDATION"
+	CodeConfigMissing    = "MISSING"
+
+	// IO Error Codes
+	CodeIOFileCreate = "FILE_CREATE"
+	CodeIOFileWrite  = "FILE_WRITE"
+	CodeIOEncoding   = "ENCODING"
+	CodeIOWrite      = "WRITE"
+	CodeIORead       = "READ"
+	CodeIOClose      = "CLOSE"
+
+	// Validation Error Codes
+	CodeValidationFormat   = "FORMAT"
+	CodeValidationFileType = "FILE_TYPE"
+	CodeValidationSize     = "SIZE_LIMIT"
+)
+
+// Predefined error constructors for common error scenarios
+
+// NewCLIMissingSourceError creates a CLI error for missing source argument.
+func NewCLIMissingSourceError() *StructuredError {
+	return NewStructuredError(ErrorTypeCLI, CodeCLIMissingSource, "usage: gibidify -source <source_directory> [--destination <output_file>] [--format=json|yaml|markdown]")
+}
+
+// NewFileSystemError creates a file system error.
+func NewFileSystemError(code, message string) *StructuredError {
+	return NewStructuredError(ErrorTypeFileSystem, code, message)
+}
+
+// NewProcessingError creates a processing error.
+func NewProcessingError(code, message string) *StructuredError {
+	return NewStructuredError(ErrorTypeProcessing, code, message)
+}
+
+// NewIOError creates an IO error.
+func NewIOError(code, message string) *StructuredError {
+	return NewStructuredError(ErrorTypeIO, code, message)
+}
+
+// NewValidationError creates a validation error.
+func NewValidationError(code, message string) *StructuredError {
+	return NewStructuredError(ErrorTypeValidation, code, message)
+}
+
+// LogError logs an error with a consistent format if the error is not nil.
+// The operation parameter describes what was being attempted.
+// Additional context can be provided via the args parameter.
+func LogError(operation string, err error, args ...any) {
+	if err != nil {
+		msg := operation
+		if len(args) > 0 {
+			// Format the operation string with the provided arguments
+			msg = fmt.Sprintf(operation, args...)
+		}
+
+		// Check if it's a structured error and log with additional context
+		if structErr, ok := err.(*StructuredError); ok {
+			logrus.WithFields(logrus.Fields{
+				"error_type": structErr.Type.String(),
+				"error_code": structErr.Code,
+				"context":    structErr.Context,
+				"file_path":  structErr.FilePath,
+				"line":       structErr.Line,
+			}).Errorf("%s: %v", msg, err)
+		} else {
+			logrus.Errorf("%s: %v", msg, err)
+		}
+	}
+}
+
+// LogErrorf logs an error with a formatted message if the error is not nil.
+// This is a convenience wrapper around LogError for cases where formatting is needed.
+func LogErrorf(err error, format string, args ...any) {
+	if err != nil {
+		LogError(format, err, args...)
+	}
+}
diff --git a/utils/errors_test.go b/utils/errors_test.go
new file mode 100644
index 0000000..1831240
--- /dev/null
+++ b/utils/errors_test.go
@@ -0,0 +1,242 @@
+package utils
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/sirupsen/logrus"
+)
+
+// captureLogOutput captures logrus output for testing
+func captureLogOutput(f func()) string {
+	var buf bytes.Buffer
+	logrus.SetOutput(&buf)
+	defer logrus.SetOutput(logrus.StandardLogger().Out)
+	f()
+	return buf.String()
+}
+
+func TestLogError(t *testing.T) {
+	tests := []struct {
+		name      string
+		operation string
+		err       error
+		args      []any
+		wantLog   string
+		wantEmpty bool
+	}{
+		{
+			name:      "nil error should not log",
+			operation: "test operation",
+			err:       nil,
+			args:      nil,
+			wantEmpty: true,
+		},
+		{
+			name:      "basic error logging",
+			operation: "failed to read file",
+			err:       errors.New("permission denied"),
+			args:      nil,
+			wantLog:   "failed to read file: permission denied",
+		},
+		{
+			name:      "error with formatting args",
+			operation: "failed to process file %s",
+			err:       errors.New("file too large"),
+			args:      []any{"test.txt"},
+			wantLog:   "failed to process file test.txt: file too large",
+		},
+		{
+			name:      "error with multiple formatting args",
+			operation: "failed to copy from %s to %s",
+			err:       errors.New("disk full"),
+			args:      []any{"source.txt", "dest.txt"},
+			wantLog:   "failed to copy from source.txt to dest.txt: disk full",
+		},
+		{
+			name:      "wrapped error",
+			operation: "database operation failed",
+			err:       fmt.Errorf("connection error: %w", errors.New("timeout")),
+			args:      nil,
+			wantLog:   "database operation failed: connection error: timeout",
+		},
+		{
+			name:      "empty operation string",
+			operation: "",
+			err:       errors.New("some error"),
+			args:      nil,
+			wantLog:   ": some error",
+		},
+		{
+			name:      "operation with percentage sign",
+			operation: "processing 50% complete",
+			err:       errors.New("interrupted"),
+			args:      nil,
+			wantLog:   "processing 50% complete: interrupted",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			output := captureLogOutput(func() {
+				LogError(tt.operation, tt.err, tt.args...)
+			})
+
+			if tt.wantEmpty {
+				if output != "" {
+					t.Errorf("LogError() logged output when error was nil: %q", output)
+				}
+				return
+			}
+
+			if !strings.Contains(output, tt.wantLog) {
+				t.Errorf("LogError() output = %q, want to contain %q", output, tt.wantLog)
+			}
+
+			// Verify it's logged at ERROR level
+			if !strings.Contains(output, "level=error") {
+				t.Errorf("LogError() should log at ERROR level, got: %q", output)
+			}
+		})
+	}
+}
+
+func TestLogErrorf(t *testing.T) {
+	tests := []struct {
+		name      string
+		err       error
+		format    string
+		args      []any
+		wantLog   string
+		wantEmpty bool
+	}{
+		{
+			name:      "nil error should not log",
+			err:       nil,
+			format:    "operation %s failed",
+			args:      []any{"test"},
+			wantEmpty: true,
+		},
+		{
+			name:    "basic formatted error",
+			err:     errors.New("not found"),
+			format:  "file %s not found",
+			args:    []any{"config.yaml"},
+			wantLog: "file config.yaml not found: not found",
+		},
+		{
+			name:    "multiple format arguments",
+			err:     errors.New("invalid range"),
+			format:  "value %d is not between %d and %d",
+			args:    []any{150, 0, 100},
+			wantLog: "value 150 is not between 0 and 100: invalid range",
+		},
+		{
+			name:    "no format arguments",
+			err:     errors.New("generic error"),
+			format:  "operation failed",
+			args:    nil,
+			wantLog: "operation failed: generic error",
+		},
+		{
+			name:    "format with different types",
+			err:     errors.New("type mismatch"),
+			format:  "expected %s but got %d",
+			args:    []any{"string", 42},
+			wantLog: "expected string but got 42: type mismatch",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			output := captureLogOutput(func() {
+				LogErrorf(tt.err, tt.format, tt.args...)
+			})
+
+			if tt.wantEmpty {
+				if output != "" {
+					t.Errorf("LogErrorf() logged output when error was nil: %q", output)
+				}
+				return
+			}
+
+			if !strings.Contains(output, tt.wantLog) {
+				t.Errorf("LogErrorf() output = %q, want to contain %q", output, tt.wantLog)
+			}
+
+			// Verify it's logged at ERROR level
+			if !strings.Contains(output, "level=error") {
+				t.Errorf("LogErrorf() should log at ERROR level, got: %q", output)
+			}
+		})
+	}
+}
+
+func TestLogErrorConcurrency(t *testing.T) {
+	// Test that LogError is safe for concurrent use
+	done := make(chan bool)
+	for i := 0; i < 10; i++ {
+		go func(n int) {
+			LogError("concurrent operation", fmt.Errorf("error %d", n))
+			done <- true
+		}(i)
+	}
+
+	// Wait for all goroutines to complete
+	for i := 0; i < 10; i++ {
+		<-done
+	}
+}
+
+func TestLogErrorfConcurrency(t *testing.T) {
+	// Test that LogErrorf is safe for concurrent use
+	done := make(chan bool)
+	for i := 0; i < 10; i++ {
+		go func(n int) {
+			LogErrorf(fmt.Errorf("error %d", n), "concurrent operation %d", n)
+			done <- true
+		}(i)
+	}
+
+	// Wait for all goroutines to complete
+	for i := 0; i < 10; i++ {
+		<-done
+	}
+}
+
+// BenchmarkLogError benchmarks the LogError function
+func BenchmarkLogError(b *testing.B) {
+	err := errors.New("benchmark error")
+	// Disable output during benchmark
+	logrus.SetOutput(bytes.NewBuffer(nil))
+	defer logrus.SetOutput(logrus.StandardLogger().Out)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		LogError("benchmark operation", err)
+	}
+}
+
+// BenchmarkLogErrorf benchmarks the LogErrorf function
+func BenchmarkLogErrorf(b *testing.B) {
+	err := errors.New("benchmark error")
+	// Disable output during benchmark
+	logrus.SetOutput(bytes.NewBuffer(nil))
+	defer logrus.SetOutput(logrus.StandardLogger().Out)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		LogErrorf(err, "benchmark operation %d", i)
+	}
+}
+
+// BenchmarkLogErrorNil benchmarks LogError with nil error (no-op case)
+func BenchmarkLogErrorNil(b *testing.B) {
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		LogError("benchmark operation", nil)
+	}
+}
diff --git a/utils/paths.go b/utils/paths.go
new file mode 100644
index 0000000..845d0ca
--- /dev/null
+++ b/utils/paths.go
@@ -0,0 +1,26 @@
+// Package utils provides common utility functions.
+package utils
+
+import (
+	"fmt"
+	"path/filepath"
+)
+
+// GetAbsolutePath returns the absolute path for the given path.
+// It wraps filepath.Abs with consistent error handling.
+func GetAbsolutePath(path string) (string, error) {
+	abs, err := filepath.Abs(path)
+	if err != nil {
+		return "", fmt.Errorf("failed to get absolute path for %s: %w", path, err)
+	}
+	return abs, nil
+}
+
+// GetBaseName returns the base name for the given path, handling special cases.
+func GetBaseName(absPath string) string {
+	baseName := filepath.Base(absPath)
+	if baseName == "." || baseName == "" {
+		return "output"
+	}
+	return baseName
+}
diff --git a/utils/paths_test.go b/utils/paths_test.go
new file mode 100644
index 0000000..fe5b80e
--- /dev/null
+++ b/utils/paths_test.go
@@ -0,0 +1,262 @@
+package utils
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestGetAbsolutePath(t *testing.T) {
+	// Get current working directory for tests
+	cwd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("Failed to get current directory: %v", err)
+	}
+
+	tests := []struct {
+		name        string
+		path        string
+		wantPrefix  string
+		wantErr     bool
+		wantErrMsg  string
+		skipWindows bool
+	}{
+		{
+			name:       "absolute path unchanged",
+			path:       cwd,
+			wantPrefix: cwd,
+			wantErr:    false,
+		},
+		{
+			name:       "relative path current directory",
+			path:       ".",
+			wantPrefix: cwd,
+			wantErr:    false,
+		},
+		{
+			name:       "relative path parent directory",
+			path:       "..",
+			wantPrefix: filepath.Dir(cwd),
+			wantErr:    false,
+		},
+		{
+			name:       "relative path with file",
+			path:       "test.txt",
+			wantPrefix: filepath.Join(cwd, "test.txt"),
+			wantErr:    false,
+		},
+		{
+			name:       "relative path with subdirectory",
+			path:       "subdir/file.go",
+			wantPrefix: filepath.Join(cwd, "subdir", "file.go"),
+			wantErr:    false,
+		},
+		{
+			name:       "empty path",
+			path:       "",
+			wantPrefix: cwd,
+			wantErr:    false,
+		},
+		{
+			name:        "path with tilde",
+			path:        "~/test",
+			wantPrefix:  filepath.Join(cwd, "~", "test"),
+			wantErr:     false,
+			skipWindows: false,
+		},
+		{
+			name:       "path with multiple separators",
+			path:       "path//to///file",
+			wantPrefix: filepath.Join(cwd, "path", "to", "file"),
+			wantErr:    false,
+		},
+		{
+			name:       "path with trailing separator",
+			path:       "path/",
+			wantPrefix: filepath.Join(cwd, "path"),
+			wantErr:    false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.skipWindows && runtime.GOOS == "windows" {
+				t.Skip("Skipping test on Windows")
+			}
+
+			got, err := GetAbsolutePath(tt.path)
+
+			if tt.wantErr {
+				if err == nil {
+					t.Errorf("GetAbsolutePath() error = nil, wantErr %v", tt.wantErr)
+					return
+				}
+				if tt.wantErrMsg != "" && !strings.Contains(err.Error(), tt.wantErrMsg) {
+					t.Errorf("GetAbsolutePath() error = %v, want error containing %v", err, tt.wantErrMsg)
+				}
+				return
+			}
+
+			if err != nil {
+				t.Errorf("GetAbsolutePath() unexpected error = %v", err)
+				return
+			}
+
+			// Clean the expected path for comparison
+			wantClean := filepath.Clean(tt.wantPrefix)
+			gotClean := filepath.Clean(got)
+
+			if gotClean != wantClean {
+				t.Errorf("GetAbsolutePath() = %v, want %v", gotClean, wantClean)
+			}
+
+			// Verify the result is actually absolute
+			if !filepath.IsAbs(got) {
+				t.Errorf("GetAbsolutePath() returned non-absolute path: %v", got)
+			}
+		})
+	}
+}
+
+func TestGetAbsolutePathSpecialCases(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("Skipping Unix-specific tests on Windows")
+	}
+
+	tests := []struct {
+		name    string
+		setup   func() (string, func())
+		path    string
+		wantErr bool
+	}{
+		{
+			name: "symlink to directory",
+			setup: func() (string, func()) {
+				tmpDir := t.TempDir()
+				target := filepath.Join(tmpDir, "target")
+				link := filepath.Join(tmpDir, "link")
+
+				if err := os.Mkdir(target, 0o755); err != nil {
+					t.Fatalf("Failed to create target directory: %v", err)
+				}
+				if err := os.Symlink(target, link); err != nil {
+					t.Fatalf("Failed to create symlink: %v", err)
+				}
+
+				return link, func() {}
+			},
+			path:    "",
+			wantErr: false,
+		},
+		{
+			name: "broken symlink",
+			setup: func() (string, func()) {
+				tmpDir := t.TempDir()
+				link := filepath.Join(tmpDir, "broken_link")
+
+				if err := os.Symlink("/nonexistent/path", link); err != nil {
+					t.Fatalf("Failed to create broken symlink: %v", err)
+				}
+
+				return link, func() {}
+			},
+			path:    "",
+			wantErr: false, // filepath.Abs still works with broken symlinks
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			path, cleanup := tt.setup()
+			defer cleanup()
+
+			if tt.path == "" {
+				tt.path = path
+			}
+
+			got, err := GetAbsolutePath(tt.path)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("GetAbsolutePath() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+
+			if err == nil && !filepath.IsAbs(got) {
+				t.Errorf("GetAbsolutePath() returned non-absolute path: %v", got)
+			}
+		})
+	}
+}
+
+func TestGetAbsolutePathConcurrency(t *testing.T) {
+	// Test that GetAbsolutePath is safe for concurrent use
+	paths := []string{".", "..", "test.go", "subdir/file.txt", "/tmp/test"}
+	done := make(chan bool)
+
+	for _, p := range paths {
+		go func(path string) {
+			_, _ = GetAbsolutePath(path)
+			done <- true
+		}(p)
+	}
+
+	// Wait for all goroutines to complete
+	for range paths {
+		<-done
+	}
+}
+
+func TestGetAbsolutePathErrorFormatting(t *testing.T) {
+	// This test verifies error message formatting
+	// We need to trigger an actual error from filepath.Abs
+	// On Unix systems, we can't easily trigger filepath.Abs errors
+	// so we'll just verify the error wrapping works correctly
+
+	// Create a test that would fail if filepath.Abs returns an error
+	path := "test/path"
+	got, err := GetAbsolutePath(path)
+	if err != nil {
+		// If we somehow get an error, verify it's properly formatted
+		if !strings.Contains(err.Error(), "failed to get absolute path for") {
+			t.Errorf("Error message format incorrect: %v", err)
+		}
+		if !strings.Contains(err.Error(), path) {
+			t.Errorf("Error message should contain original path: %v", err)
+		}
+	} else {
+		// Normal case - just verify we got a valid absolute path
+		if !filepath.IsAbs(got) {
+			t.Errorf("Expected absolute path, got: %v", got)
+		}
+	}
+}
+
+// BenchmarkGetAbsolutePath benchmarks the GetAbsolutePath function
+func BenchmarkGetAbsolutePath(b *testing.B) {
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = GetAbsolutePath("test/path/file.go")
+	}
+}
+
+// BenchmarkGetAbsolutePathAbs benchmarks with already absolute path
+func BenchmarkGetAbsolutePathAbs(b *testing.B) {
+	absPath := "/home/user/test/file.go"
+	if runtime.GOOS == "windows" {
+		absPath = "C:\\Users\\test\\file.go"
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = GetAbsolutePath(absPath)
+	}
+}
+
+// BenchmarkGetAbsolutePathCurrent benchmarks with current directory
+func BenchmarkGetAbsolutePathCurrent(b *testing.B) {
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = GetAbsolutePath(".")
+	}
+}