fallow-core 2.3.0

npx fallow

 Dead code   3 unused files, 12 unused exports, 2 unused deps       18ms
 Duplication 4 clone groups (2.1% of codebase)                      31ms
 Complexity  7 functions exceed thresholds                           4ms
 Total       26 issues across 847 files                             53ms

84 framework plugins. No Node.js runtime. No config file needed.

Install

npx fallow                  # Run without installing
npm install -g fallow       # Or install globally (macOS, Linux, Windows)
cargo install fallow-cli    # Or via Cargo

Commands

fallow                      # Run all three analyses
fallow dead-code            # Dead code only
fallow dupes                # Duplication only
fallow health               # Complexity only
fallow fix --dry-run        # Preview auto-removal of dead exports and deps
fallow watch                # Re-analyze on file changes

Dead code

Finds unused files, exports, dependencies, types, enum members, class members, unresolved imports, unlisted dependencies, duplicate exports, circular dependencies, and type-only dependencies.

fallow dead-code                          # All dead code issues
fallow dead-code --unused-exports         # Only unused exports
fallow dead-code --circular-deps          # Only circular dependencies
fallow dead-code --production             # Exclude test/dev files
fallow dead-code --changed-since main     # Only changed files (for PRs)

Duplication

Finds copy-pasted code blocks across your codebase. Suffix-array algorithm -- no quadratic pairwise comparison.

fallow dupes                              # Default (mild mode)
fallow dupes --mode semantic              # Catch clones with renamed variables
fallow dupes --skip-local                 # Only cross-directory duplicates
fallow dupes --trace src/utils.ts:42      # Show all clones of code at this location

Four detection modes: strict (exact tokens), mild (default, AST-based), weak (different string literals), semantic (renamed variables and literals).

Complexity

Surfaces the most complex functions in your codebase and identifies where to spend refactoring effort.

fallow health                             # Functions exceeding thresholds
fallow health --top 20                    # 20 most complex functions
fallow health --file-scores               # Per-file maintainability index (0-100)
fallow health --hotspots                  # Riskiest files (git churn x complexity)
fallow health --targets                   # Ranked refactoring recommendations
fallow health --changed-since main        # Only changed files

CI integration

# GitHub Action
- uses: fallow-rs/fallow@v1

# GitLab CI — include the template and extend
include:
  - remote: 'https://raw.githubusercontent.com/fallow-rs/fallow/main/ci/gitlab-ci.yml'
fallow:
  extends: .fallow

# Or run directly on any CI
- run: npx fallow --ci

--ci enables SARIF output, quiet mode, and non-zero exit on issues. Also supports:

• --changed-since main -- analyze only files touched in a PR
• --baseline / --save-baseline -- fail only on new issues
• --format sarif -- upload to GitHub Code Scanning
• --format codeclimate -- GitLab Code Quality inline MR annotations
• --format annotations -- GitHub Actions inline PR annotations (no Action required)
• --format json / --format markdown -- for custom workflows

Both the GitHub Action and GitLab CI template auto-detect your package manager (npm/pnpm/yarn) from lock files, so install/uninstall commands in review comments match your project.

Adopt incrementally -- surface issues without blocking CI, then promote when ready:

{ "rules": { "unused-files": "error", "unused-exports": "warn", "circular-dependencies": "off" } }

GitLab CI rich MR comments

The GitLab CI template can post rich comments directly on merge requests -- summary comments with collapsible sections and inline review discussions with suggestion blocks.

In MR pipelines, --changed-since is set automatically to scope analysis to changed files. Previous fallow comments are cleaned up on re-runs.

The comment merging pipeline groups unused exports per file and deduplicates clone reports, keeping MR threads readable.

A GITLAB_TOKEN (PAT with api scope) is recommended for full features (suggestion blocks, cleanup of previous comments). CI_JOB_TOKEN works for posting but cannot delete comments from prior runs.

# .gitlab-ci.yml — full example with rich MR comments
include:
  - remote: 'https://raw.githubusercontent.com/fallow-rs/fallow/main/ci/gitlab-ci.yml'

fallow:
  extends: .fallow
  variables:
    FALLOW_COMMENT: "true"       # Summary comment with collapsible sections
    FALLOW_REVIEW: "true"        # Inline discussions with suggestion blocks
    FALLOW_MAX_COMMENTS: "30"    # Cap inline comments (default: 50)
    FALLOW_FAIL_ON_ISSUES: "true"

Configuration

Works out of the box. When you need to customize, create .fallowrc.json or run fallow init:

// .fallowrc.json
{
  "$schema": "https://raw.githubusercontent.com/fallow-rs/fallow/main/schema.json",
  "entry": ["src/workers/*.ts", "scripts/*.ts"],
  "ignorePatterns": ["**/*.generated.ts"],
  "ignoreDependencies": ["autoprefixer"],
  "rules": {
    "unused-files": "error",
    "unused-exports": "warn",
    "unused-types": "off"
  },
  "health": {
    "maxCyclomatic": 20,
    "maxCognitive": 15
  }
}

TOML also supported (fallow init --toml). Migrating from knip or jscpd? Run fallow migrate.

See the full configuration reference for all options.

Framework plugins

84 built-in plugins detect entry points and used exports for your framework automatically.

Full plugin list -- missing one? Add a custom plugin or open an issue.

Editor & AI support

• VS Code extension -- tree views, status bar, one-click fixes, auto-download LSP binary (Marketplace)
• LSP server -- real-time diagnostics, hover info, code actions, Code Lens with reference counts
• MCP server -- AI agent integration for Claude Code, Cursor, Windsurf (fallow-skills)

Performance

Benchmarked on real open-source projects (median of 5 runs, Apple M5).

Dead code: fallow vs knip

knip errors out on next.js. fallow completes in under 2 seconds.

Duplication: fallow vs jscpd

No TypeScript compiler, no Node.js runtime. How it works | Reproduce benchmarks

Suppressing findings

// fallow-ignore-next-line unused-export
export const keepThis = 1;

// fallow-ignore-file
// Suppress all issues in this file

Also supports /** @public */ JSDoc tags for library exports consumed externally.

Limitations

fallow uses syntactic analysis -- no type information. This is what makes it fast, but type-level dead code is out of scope. Use inline suppression comments or ignoreExports for edge cases.

Documentation

• Getting started
• Configuration reference
• CI integration guide
• Migrating from knip
• Plugin authoring guide

Contributing

Missing a framework plugin? Found a false positive? Open an issue.

cargo build --workspace && cargo test --workspace

License

MIT