Fallow: codebase intelligence for TypeScript repositories

Fallow is a single Rust binary that finds dead code, duplication, complexity hotspots, and boundary violations across TypeScript and JavaScript codebases. Static analysis is free, sub-second, and ships with 95 auto-detecting plugins (Next.js, Vite, Turbo, Tailwind, Storybook, Jest, pnpm catalogs, etc.). The paid runtime layer (@fallow-cli/beacon SDK + fallow cloud) merges production traffic into the same health report so cold code can be deleted with evidence.

When This Skill Applies

Use proactively before any cleanup/refactor pass on a TS/JS monorepo, when the user describes "I think we have a lot of dead code", or whenever a code-quality task is scoped to a JS/TS project — even when they never name fallow. The per-tool documentation for each MCP capability lives in the fallow MCP server's own instruction block; this skill is the trigger surface plus T3 operating patterns, not a duplicate of that catalog.

When to use

• Dead-code audits before a release or refactor (unused files, exports, types, deps)
• "Why is this codebase so heavy?" — duplicates, complexity hotspots, churn-weighted refactor targets
• PR quality gate (fallow audit --base <branch>) for changed-files-only review with verdict
• Architecture boundary checks (layered / hexagonal / feature-sliced / bulletproof presets)
• Feature-flag inventory (env gates, SDK calls, config objects)
• Wiring up cloud runtime intelligence (beacon SDK + dashboard)
• Migrating off knip or jscpd
• Investigating why a specific export, file, or dependency is flagged (--trace* family)