Fallow

What is Fallow?

Fallow is a codebase analysis tool for TypeScript and JavaScript. A single run checks for dead code, duplicated logic, and maintainability problems such as complexity hot spots.

It complements a linter: a linter examines individual files for suspicious syntax and style, while Fallow follows relationships across the project to find unused files, exports, types, and dependencies.

Installation

Install Fallow as a development dependency so everyone on the project uses the same version:

pnpm add --save-dev fallow

Wire the local binary into package.json:

package.json

{
  "scripts": {
    "fallow": "fallow"
  }
}

Run the complete analysis with:

pnpm fallow

The bare command runs all three analysis groups. During focused work, you can run pnpm fallow dead-code, pnpm fallow dupes, or pnpm fallow health.

Configuration

Fallow works without configuration. When a framework or build tool loads a file by convention, however, static analysis may not see the connection. Create a .fallowrc.json and add only those paths to ignorePatterns:

.fallowrc.json

{
  "$schema": "https://raw.githubusercontent.com/fallow-rs/fallow/main/schema.json",
  "entry": ["main.ts"],
  "ignorePatterns": ["vite.config.ts"],
  "ignoreDependencies": ["@fontsource-variable/atkinson-hyperlegible-next"]
}

The $schema entry enables validation and editor completion.

Practical workflow

1. Run pnpm fallow.
2. Review each finding before deleting code or dependencies.
3. Fix genuine findings in small, testable changes.
4. Add a focused ignore only when usage depends on a convention Fallow cannot discover.
5. Re-run the analysis until its output is useful and understood.

For automatic cleanup, preview changes first with pnpm fallow fix --dry-run. Commit or stash unrelated work before applying a fix without --dry-run.

References

• Fallow installation
• Fallow quick start
• Migrating from Knip
• Fallow configuration