fallow: codebase intelligence for TypeScript and JavaScript

This page gets you from zero to a useful result fast. Everyone starts the same way. Branch off at the end.

1. Run Fallow

From your project root:

npx fallow

That runs three analyses in one pass:

Dead code: unused files, exports, dependencies, cycles, boundaries, and more
Duplication: repeated logic across files
Health: complexity hotspots and refactor targets

Built-in plugins cover Next.js, Vite, Ember, Wuchale, Jest, Tailwind, PandaCSS, Contentlayer, tap, tsd, and more. No configuration needed for the first run.

2. Run the focused commands you’ll use most

npx fallow dead-code          # Cleanup candidates
npx fallow dupes              # Repeated logic
npx fallow health             # Complexity and refactor targets
npx fallow review             # Advisory review brief over changed files (always exits 0)
npx fallow fix --dry-run      # Preview automatic cleanup

3. Understand the output

Dead code

Use this when you want cleanup candidates.

npx fallow dead-code

Reports unused files, exports, types, dependencies, circular deps, and boundary violations. See the dead code guide.

Duplication

Use this when repeated logic is spreading.

npx fallow dupes

Default mild mode catches AST-based duplicates. Add --mode semantic to also catch clones with renamed variables. See the duplication guide.

Health

Use this when you want to prioritize refactors.

npx fallow health

Reports complexity findings, per-file maintainability, hotspots, and ranked refactor targets. See the health explanation.

Fix preview

Use this before deleting anything automatically.

npx fallow fix --dry-run

When you’re ready, drop --dry-run. See the auto-fix guide.

Cleaning up or refactoring TypeScript? Add --type-aware when aliases, re-exports, class contracts, packages, or exact consumers affect the decision. This is an optional, slower semantic pass. See Type-aware TypeScript analysis.

4. Pick your next step

Existing repo with backlog? Read Adopt Fallow in an existing repo for a structured cleanup path, then come back here to wire up CI or VS Code.

Use it in VS Code

Real-time diagnostics, Code Lens above exports, and one-click fixes.

Use it in CI

Turn Fallow into a PR and merge gate with SARIF or MR annotations.

Use it from agents

Add MCP for structured tool calling from Claude Code, Cursor, and more.

Add runtime evidence

Layer production execution data into fallow health.

Optional: create a config

Fallow works without a config file. When you want to customize, run:

fallow init

This auto-detects your project structure and generates a tailored config. It also adds .fallow/ to your .gitignore.

{
  "$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"
  }
}

entry = ["src/workers/*.ts", "scripts/*.ts"]
ignorePatterns = ["**/*.generated.ts"]

[rules]
unused-files = "error"
unused-exports = "warn"
unused-types = "off"

Migrating from knip or jscpd? Run fallow migrate, or see the knip or jscpd guides.

Optional: runtime intelligence

Fallow’s static layer is free and open source. If you want to know what actually executed in production, add the runtime layer:

npx fallow license activate --trial --email you@company.com
npx fallow coverage setup
npx fallow health --runtime-coverage ./coverage

Before you do that, read Static vs runtime intelligence for the mental model, then the runtime coverage guide for setup details.

Optional: workflow-specific setup

Agents

Any agent that can run a shell command can use Fallow. Use --format json for structured output:

npx fallow --format json
npx fallow dead-code --format json
npx fallow fix --dry-run --format json

If your agent supports MCP, add structured tool calling:

{
  "mcpServers": {
    "fallow": {
      "command": "fallow-mcp"
    }
  }
}

This assumes fallow-mcp is on your PATH. If fallow is a project devDependency, the binary lives in node_modules/.bin/ instead, so launch it through your package manager: set "command": "npx" with "args": ["fallow-mcp"] (or pnpm exec / yarn / bunx). See the MCP integration guide.

Humans

Install the VS Code extension for real-time diagnostics, Code Lens above exports, and one-click fixes:

code --install-extension fallow-rs.fallow-vscode

See the VS Code integration guide.

CI

Use the GitHub Action, the GitLab template, or npx fallow --ci on any CI:

GitHub Action
GitLab CI
Other CI

- uses: fallow-rs/fallow@v3
  with:
    format: sarif

include:
  - remote: 'https://raw.githubusercontent.com/fallow-rs/fallow/main/ci/gitlab-ci.yml'

fallow:
  extends: .fallow

- run: npx fallow --ci

See the CI integration guide.

Next steps

Analysis overview

What Fallow analyzes, at a glance.

Configuration

Customize entry points, rules, and ignore patterns.

Explanations

Mental models for how Fallow works.

CLI reference

Every command and flag.

Getting Started

Analysis

Cloud

Configuration

Integrations

Explanations

Frameworks

Migration

Quick start

1. Run Fallow

2. Run the focused commands you’ll use most

3. Understand the output

Dead code

Duplication

Health

Fix preview

4. Pick your next step

Use it in VS Code

Use it in CI

Use it from agents

Add runtime evidence

Optional: create a config

Optional: runtime intelligence

Optional: workflow-specific setup

Agents

Humans

CI

Next steps

Analysis overview

Configuration

Explanations

CLI reference

​1. Run Fallow

​2. Run the focused commands you’ll use most

​3. Understand the output

​Dead code

​Duplication

​Health

​Fix preview

​4. Pick your next step

Use it in VS Code

Use it in CI

Use it from agents

Add runtime evidence

​Optional: create a config

​Optional: runtime intelligence

​Optional: workflow-specific setup

​Agents

​Humans

​CI

​Next steps

Analysis overview

Configuration

Explanations

CLI reference

1. Run Fallow

2. Run the focused commands you’ll use most

3. Understand the output

Dead code

Duplication

Health

Fix preview

4. Pick your next step

Optional: create a config

Optional: runtime intelligence

Optional: workflow-specific setup

Agents

Humans

CI

Next steps