fallow

The codebase analyzer for TypeScript and JavaScript, built in Rust.

Unused code, circular dependencies, code duplication, complexity hotspots, and architecture boundary violations. Found in seconds, not minutes. fallow analyzes your codebase for unused files, exports, dependencies, and types, detects circular dependencies, finds duplicated code blocks, surfaces complexity hotspots, and enforces architecture boundaries. 5-41x faster than knip v5 (2-18x faster than knip v6), 8-29x faster than jscpd for duplication detection, with no Node.js runtime dependency.

Installation

npm install -g fallow

Usage

fallow                           # All analyses -- zero config, sub-second
fallow dead-code                 # Unused code only
fallow dupes                     # Duplication detection -- find copy-paste clones
fallow dupes --mode semantic     # Catch clones with renamed variables
fallow health                    # Complexity metrics -- cyclomatic + cognitive
fallow fix --dry-run             # Preview auto-removal of unused exports and deps

What it finds

• Unused files -- not reachable from any entry point
• Unused exports -- exported symbols never imported elsewhere
• Unused types -- type aliases and interfaces never referenced
• Unused dependencies -- packages in dependencies never imported
• Unused devDependencies -- dev packages not referenced
• Unused enum members -- enum values never referenced
• Unused class members -- class methods and properties never referenced (tracks instance usage: const svc = new MyService(); svc.greet() counts greet as used)
• Unresolved imports -- import specifiers that cannot be resolved
• Unlisted dependencies -- imported packages missing from package.json
• Duplicate exports -- same symbol exported from multiple modules
• Circular dependencies -- import cycles in the module graph
• Type-only dependencies -- production deps only used via import type

Code duplication

fallow dupes                       # Default: mild mode
fallow dupes --mode semantic       # Catch clones with renamed variables
fallow dupes --threshold 5         # Fail CI if duplication exceeds 5%
fallow dupes --save-baseline       # Save current duplication as baseline

4 detection modes (strict, mild, weak, semantic), clone family grouping with refactoring suggestions, baseline tracking, and cross-language TS/JS matching.

Framework support

84 built-in plugins covering Next.js, Nuxt, Remix, SvelteKit, Gatsby, Astro, Angular, NestJS, Vite, Webpack, Vitest, Jest, Playwright, Cypress, Storybook, ESLint, TypeScript, Tailwind, Prisma, Drizzle, Turborepo, and many more. Auto-detected from your package.json.

Configuration

Create a config file in your project root, or run fallow init:

// .fallowrc.json
{
  "$schema": "https://raw.githubusercontent.com/fallow-rs/fallow/main/schema.json",
  "entry": ["src/workers/*.ts", "scripts/*.ts"],
  "ignorePatterns": ["**/*.generated.ts"],
  "rules": {
    "unused-files": "error",
    "unused-exports": "warn",
    "unused-types": "off"
  }
}

Also supports TOML (fallow init --toml creates fallow.toml).

Documentation

• Full documentation
• GitHub repository
• Plugin Authoring Guide

License

MIT