# Fallow — TypeScript Codebase Intelligence Analyzer in Rust

> A Rust-native static analysis tool that finds unused code, duplicates, circular dependencies, and complexity hotspots in TypeScript and JavaScript projects.

## Install

Save in your project root:

# Fallow — TypeScript Codebase Intelligence Analyzer in Rust

## Quick Use
```bash
npx fallow
# or install globally
npm install -g fallow
```
```bash
fallow analyze ./src
```

## Introduction
Fallow is a Rust-native codebase intelligence tool for TypeScript and JavaScript projects. It detects unused exports, duplicate code, circular dependencies, and complexity hotspots in sub-second time, helping teams keep large codebases clean and maintainable.

## What Fallow Does
- Identifies unused exports, dead code, and unreferenced files across a TypeScript/JavaScript project
- Detects copy-pasted code blocks and near-duplicate implementations
- Maps circular dependency chains and visualizes module dependency graphs
- Calculates complexity metrics to highlight hotspots that may need refactoring
- Enforces architecture boundaries between modules or packages in a monorepo

## Architecture Overview
Fallow uses the oxc parser (a fast Rust-based JavaScript/TypeScript parser) to build an AST from source files. It constructs a dependency graph by resolving imports and exports, then runs multiple analysis passes: reachability analysis for dead code detection, token-based similarity for duplication, cycle detection for circular dependencies, and metric aggregation for complexity scoring. The Rust implementation keeps full-project analysis under one second for most codebases.

## Self-Hosting & Configuration
- Install via npm (`npx fallow` or `npm install -g fallow`) or download the Rust binary directly
- Run `fallow analyze` in a project root to scan all TypeScript and JavaScript files
- Configure analysis rules in a `fallow.config.json` or via CLI flags
- Exclude paths or files with glob patterns in the configuration
- Integrate into CI pipelines to enforce code quality thresholds on pull requests

## Key Features
- Sub-second analysis speed on most projects thanks to the Rust implementation
- Zero configuration needed for basic unused code and circular dependency detection
- Framework-aware analysis understands Next.js, React, and common project structures
- Architecture boundary enforcement prevents unwanted cross-module dependencies
- JSON and human-readable output formats for CI integration and developer workflows

## Comparison with Similar Tools
- **ESLint** — Rule-based linter for code style; Fallow focuses on structural analysis like dead code and duplication
- **Knip** — JavaScript dead code finder; Fallow adds duplication detection and complexity analysis in a faster runtime
- **Madge** — Circular dependency visualization; Fallow includes this plus dead code and duplication analysis
- **SonarQube** — Enterprise code quality platform; Fallow is lighter and specialized for TypeScript
- **depcheck** — Finds unused npm dependencies; Fallow analyzes source-level exports and imports

## FAQ
**Q: Does it support plain JavaScript or only TypeScript?**
A: Both. Fallow analyzes `.ts`, `.tsx`, `.js`, `.jsx`, `.mjs`, and `.cjs` files.

**Q: How fast is it on large codebases?**
A: Most projects analyze in under one second. The Rust implementation and oxc parser make it significantly faster than Node.js-based alternatives.

**Q: Can I use it in a monorepo?**
A: Yes. Fallow supports monorepo structures and can enforce architecture boundaries between packages.

**Q: Does it support auto-fixing issues?**
A: Fallow reports findings but does not auto-remove code. Deletion is left to the developer to avoid unintended side effects.

## Sources
- https://github.com/fallow-rs/fallow

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Source: https://tokrepo.com/en/workflows/asset-876c30b2
Author: AI Open Source