Fallow: Codebase Intelligence for TypeScript & JavaScript

Rust-native. Zero config. Sub-second.

Fallow is codebase intelligence for TypeScript and JavaScript. It analyzes your codebase to find unused code, duplicated logic, complexity issues, and architecture drift across your entire project — not just individual files.

The core insight: Linters check files. TypeScript checks types. Fallow checks the codebase by building a module graph across your entire project. This enables it to find problems that file-local tools cannot.

What Fallow Finds

Dead code: unused files, exports, dependencies, types, cycles, boundary violations, stale suppressions, GraphQL documents linked by `#import`, plus opt-in API hygiene checks such as private type leaks
Duplication: repeated code blocks from exact to semantic clones
Complexity: high-risk functions, file scores, hotspots, and refactor targets
Architecture drift: boundary violations across layers and modules

How Agents Use Fallow

Agents do not need to guess from limited context. They can call Fallow directly via the CLI or MCP:

Generate or edit code
Run `fallow --format json`
Inspect dead code, duplication, health findings, and per-issue `actions`

Performance

Dead Code: Fallow vs knip

Project	Files	Fallow	knip v5	knip v6	vs v5	vs v6
zod	174	25ms	650ms	330ms	26x	13x
fastify	286	27ms	933ms	222ms	34x	8x
preact	244	200ms	911ms	2.15s	5x	11x

Duplication: Fallow vs jscpd

Project	Files	Fallow	jscpd	Speedup
fastify	286	76ms	1.96s	26x
vue/core	522	124ms	3.11s	25x
next.js	20,416	2.89s	24.37s	8x

Framework Plugins

91 built-in plugins detect entry points, convention exports, config-defined aliases, and template-visible usage for your framework automatically.

Frameworks

Next.js, Nuxt, Remix, Qwik, SvelteKit, Gatsby, Astro, Angular, NestJS, Expo, Expo Router, Electron

Bundlers

Vite, Webpack, Rspack, Rsbuild, Rollup, Rolldown, Tsup, Tsdown, Parcel

Editor & AI Support

VS Code extension: tree views, status bar, one-click fixes, auto-download LSP binary
LSP server: real-time diagnostics, hover info, code actions, Code Lens with reference counts
Agent Skill + MCP server: version-matched AI agent guidance ships in the npm package, with MCP integration for Claude Code, Codex, Cursor, Windsurf, and other agents
JSON `actions` array: every issue in `--format json` output includes fix suggestions with `auto_fixable` flag, so agents can self-correct

Runtime Intelligence (Optional)

Static analysis answers: what is connected to what? Runtime intelligence answers: what actually ran?

Fallow Runtime is the optional paid team layer. It uses runtime coverage as the collection engine (V8 dumps via `NODE_V8_COVERAGE=...` and Istanbul `coverage-final.json` files), then merges that evidence into `fallow health` so teams and coding agents can:

Review changes on hot production paths more carefully
Delete cold code with stronger evidence

Install

npm install --save-dev fallow   # or: pnpm add -D fallow / yarn add -D fallow / bun add -d fallow

# For one-off CLI use
npx fallow

# Rust users
cargo install fallow-cli

# Programmatic Node API
import { Fallow } from 'fallow';
const fallow = new Fallow();
const result = await fallow.analyze();

Quick Start

# Dead code + duplication + health
fallow

# Specific checks
fallow dead-code          # Cleanup candidates
fallow dupes              # Repeated logic
fallow health             # Complexity + refactor targets

# Combined mode
fallow --production-health

CI Integration

# GitHub Action
- uses: fallow-rs/fallow@v2

# GitLab CI
include:
  - remote: https://github.com/fallow-rs/fallow/raw/main/.gitlab-ci.yml

# Quality gate
fallow audit --base HEAD~3