Fallow - Codebase Health

April 2, 2026

Version updated for https://github.com/fallow-rs/fallow to version v2.9.0.

This action is used across all versions by 1 repositories.

Action Type

This is a Composite action.

Go to the GitHub Marketplace to find the latest changes.

Action Summary

This GitHub Action, “Fallow,” is a codebase analyzer designed for TypeScript and JavaScript projects. It automates the detection of unused code, duplicate code blocks, and overly complex functions, helping developers optimize their codebases by identifying inefficiencies and architectural issues. Key capabilities include fast Rust-native analysis with zero configuration, dead code removal previews, and real-time monitoring for code changes.

What’s Changed

Architecture boundary violations

Fallow now enforces architecture boundaries. Define zones (glob patterns mapping directories to layers) and rules (which zones may import from which). Violations are caught at the import site.

{
  "boundaries": {
    "preset": "bulletproof"
  }
}

Built-in presets

Preset	Zones	Pattern
`layered`	presentation, application, domain, infrastructure	Classic N-tier
`hexagonal`	adapters, ports, domain	Ports & adapters
`feature-sliced`	app, pages, widgets, features, entities, shared	Strict downward imports
`bulletproof`	app, features, shared, server	Dominant React/Next.js pattern

Presets auto-detect rootDir from tsconfig.json and generate zone patterns like src/{zone}/**. User zones and rules merge on top of preset defaults.

Inspect with `fallow list --boundaries`

Boundaries: 4 zones, 4 rules

Zones:
  app                  3 files  src/app/**
  features             12 files src/features/**
  shared               8 files  src/components/**, src/hooks/**, src/lib/**, ...
  server               4 files  src/server/**

Rules:
  app                  → features, shared, server
  features             → shared, server
  server               → shared
  shared               (isolated — no imports allowed)

Full integration

All 6 output formats (human, JSON, SARIF, compact, markdown, CodeClimate)
Inline suppression: // fallow-ignore-next-line boundary-violation
LSP diagnostics and code actions
GitHub Action annotations and review comments
GitLab CI review comments
MCP server integration
--boundary-violations filter for fallow dead-code

Other changes

Fixed: rest patterns in destructured exports (export const { a, ...rest } = obj)
Updated: oxc dependency upgrade (7 crates)

Full Changelog: https://github.com/fallow-rs/fallow/compare/v2.8.1...v2.9.0