Deterministic codebase intelligence for TypeScript and JavaScript.
Quality, risk, architecture, dependencies, duplication, and safe cleanup evidence for humans, CI, and agents.
Static analysis is free and open source. Optional runtime intelligence (Fallow Runtime) adds production execution evidence.
Rust-native. Zero config. Sub-second. No AI inside the analyzer.
Fallow turns a JS/TS repository into a trusted quality report: health score, changed-code risk, hotspots, duplication, architecture issues, dependency hygiene, and cleanup opportunities. It helps you answer:
- What changed?
- What got riskier?
- What should I review?
- What should I refactor?
- What can be safely removed?
Fallow is built for maintainers, CI pipelines, editors, and AI agents that need structured evidence instead of guesses. No AI inside the analyzer. Fallow produces deterministic findings, typed output contracts, and traceable explanations that downstream tools can trust.
Linters check files. TypeScript checks types. Fallow checks the codebase.
- Static intelligence (free, MIT). Unused files, exports, types, dependencies, circular imports, code duplication, complexity hotspots, architecture boundaries, feature-flag usage. Rust-native, sub-second on most projects, 100 framework plugins, JSON / SARIF / CodeClimate / markdown outputs, CI + editor + MCP integrations.
- Runtime intelligence (paid, Fallow Runtime). Production execution evidence merged into the same
fallow healthreport. Hot paths, cold paths, runtime-backed deletion confidence, runtime-weighted health, stale-flag evidence, trends, alerts, and shared team workflows.
Static analysis is free and open source. Runtime intelligence is the paid team layer.
npx fallow audit # Changed-code risk gate for PRs
npx fallow # Full codebase analysis: cleanup + duplication + health
npx fallow health # Quality score, hotspots, refactor targets| Repo | What it is |
|---|---|
| fallow | The CLI, LSP, MCP server, GitHub Action, and VS Code extension. Rust-native, MIT. |
| docs | docs.fallow.tools (Mintlify). |
| fallow-skills | Agent Skills pack for Claude Code, Cursor, Codex, Gemini CLI, Copilot, Windsurf, Amp, and 30+ more. |
| fallow-cov-protocol | Wire contract between the fallow CLI and Fallow Runtime's production-coverage sidecar. |
| oxc-coverage-instrument | Istanbul-compatible coverage instrumentation on the Oxc AST. Powers browser coverage collection. |
Fallow gives AI agents structured repo truth instead of forcing them to infer everything from grep. Every issue in --format json carries a machine-actionable actions array with an auto_fixable flag, so agents can self-correct before opening a PR. MCP server, LSP, and a version-matched Agent Skill ship in the npm package for Claude Code, Codex, Cursor, Windsurf, and other agents.
- Delete cold code with runtime-backed confidence, not guesses.
- Review hot-path changes with evidence, not reviewer instinct.
- Prioritize refactors by traffic and complexity together.
- Retire stale flags from what ran in practice, not what's written.
Issues and PRs welcome across every repo in the org. Start with the main fallow issue tracker or check discussions.