fallow: codebase intelligence for TypeScript and JavaScript

fallow dead-code performs dead code analysis on your TypeScript project. It builds a module graph from your and reports anything that isn’t reachable. Finding dead code requires building a complete module graph. Fallow does this deterministically in milliseconds, giving agents, developers, and CI pipelines the same reliable results.

fallow dead-code

Issue types

Fallow detects 16 types of dead code:

Issue type	Description
Unused files	Files not reachable from any entry point
Unused exports	Exported symbols never imported elsewhere
Unused types	Type aliases and interfaces never referenced
Unused dependencies	Packages in `dependencies` never imported or used as script binaries
Unused devDependencies	Packages in `devDependencies` never imported or used as script binaries
Unused optionalDependencies	Packages in `optionalDependencies` never imported or used as script binaries
Unused enum members	Enum values never referenced
Unused class members	Class methods and properties never referenced outside their class, with inheritance tracking, decorator exclusion, and framework lifecycle allowlists
Unresolved imports	Import specifiers that cannot be resolved
Unlisted dependencies	Imported packages missing from `package.json`
Duplicate exports	Same symbol exported from multiple modules
Circular dependencies	Modules that import each other directly or transitively
Boundary violations	Imports that cross user-defined architecture zone boundaries
Type-only dependencies	Production dependencies only imported via `import type` (should be devDependencies)
Test-only dependencies	Production dependencies only imported by test files (should be devDependencies)
Stale suppressions	`fallow-ignore` comments or `@expected-unused` JSDoc tags that no longer match any issue

Most projects find 50+ unused exports on first run. Start with --unused-exports for the most impactful cleanup.

Here’s what typical output looks like when fallow finds multiple issue types:

$ fallow dead-code

● Unused files (9)
  scripts/check-db.ts
  src/features/forecasting/hooks/useCashFlowForecast.ts
  src/features/forecasting/hooks/useIncomeForecast.ts
  src/features/forecasting/hooks/useTargetProgress.ts
  src/features/forecasting/hooks/useYearComparison.ts
  ... and 4 more
  Files not imported or referenced by any entry point — https://docs.fallow.tools/explanations/dead-code#unused-files

● Unused exports (24)
  test/component-helpers.tsx (5)
    :33 ThemeContext
    :58 ToastContext
    :1 within (re-export)
    :1 waitFor (re-export)
    :1 act (re-export)
  src/server/jobs/queue.ts (3)
    :61 enqueueJobDelayed
    :206 sweepStuckProcessingJobs
    :276 getDeadLetterJobs
  Exported symbols with zero references — https://docs.fallow.tools/explanations/dead-code#unused-exports

✗ 401 issues (0.16s)

Filtering by issue type

Report only specific issue types:

fallow dead-code --unused-files
fallow dead-code --unused-exports --unused-types
fallow dead-code --unresolved-imports --unlisted-deps

Output formats

Colored terminal output designed for readability.

fallow dead-code --format human

src/components/Card/index.ts
  unused-export  CardFooter  (line 1)

src/server/jobs/queue.ts
  unused-export  enqueueJobDelayed  (line 61)
  unused-export  sweepStuckProcessingJobs  (line 206)

src/server/jobs/worker.ts
  unused-file  Not reachable from any entry point

Found 401 issues (17 errors, 384 warnings)

Machine-readable JSON for scripting and tooling integration.

fallow dead-code --format json

{
  "schema_version": 3,
  "version": "2.66.2",
  "elapsed_ms": 160,
  "total_issues": 401,
  "unused_files": [
    { "path": "src/server/jobs/worker.ts" }
  ],
  "unused_exports": [
    {
      "path": "src/server/jobs/queue.ts",
      "export_name": "enqueueJobDelayed",
      "is_type_only": false,
      "line": 61,
      "col": 0,
      "span_start": 1420,
      "is_re_export": false
    }
  ],
  "unused_dependencies": [
    {
      "package_name": "@trpc/react-query",
      "location": "dependencies",
      "path": "package.json",
      "line": 18,
      "used_in_workspaces": ["apps/web"]
    }
  ]
}

format for GitHub Code Scanning and other static analysis tools.

fallow dead-code --format sarif

{
  "$schema": "https://json.schemastore.org/sarif-2.1.0.json",
  "version": "2.66.2",
  "runs": [{
    "tool": { "driver": { "name": "fallow", "version": "2.66.2" } },
    "results": [
      {
        "ruleId": "fallow/unused-export",
        "level": "error",
        "message": { "text": "Export 'enqueueJobDelayed' is never imported by other modules" },
        "locations": [{
          "physicalLocation": {
            "artifactLocation": { "uri": "src/server/jobs/queue.ts" },
            "region": { "startLine": 61, "startColumn": 1 }
          }
        }]
      }
    ]
  }]
}

One-line-per-issue output, ideal for grep and editor integration.

fallow dead-code --format compact

unused-file:src/server/jobs/worker.ts
unused-file:src/server/jobs/cron.ts
unused-export:src/server/jobs/queue.ts:61:enqueueJobDelayed
unused-export:src/components/Card/index.ts:1:CardFooter

Formatted markdown output for PR comments and documentation.

fallow dead-code --format markdown

## Fallow: 4 issues found

### Unused files (2)

- `src/server/jobs/worker.ts`
- `src/server/jobs/cron.ts`

### Unused exports (2)

- `src/server/jobs/queue.ts`
  - :61 `enqueueJobDelayed`
  - :206 `sweepStuckProcessingJobs`

Pipe directly to gh pr comment:

fallow dead-code --format markdown | gh pr comment --body-file -

CodeClimate JSON for GitLab Code Quality inline MR annotations.

fallow dead-code --format codeclimate

[
  {
    "type": "issue",
    "check_name": "fallow/unused-file",
    "description": "File is not reachable from any entry point",
    "categories": ["Bug Risk"],
    "severity": "major",
    "fingerprint": "a1b2c3d4e5f67890",
    "location": {
      "path": "src/server/jobs/worker.ts",
      "lines": { "begin": 1 }
    }
  },
  {
    "type": "issue",
    "check_name": "fallow/unused-export",
    "description": "Export 'enqueueJobDelayed' is never imported by other modules",
    "categories": ["Bug Risk"],
    "severity": "major",
    "fingerprint": "b2c3d4e5f6789012",
    "location": {
      "path": "src/server/jobs/queue.ts",
      "lines": { "begin": 61 }
    }
  }
]

Use in GitLab CI for inline annotations:

fallow:
  script: npx fallow dead-code --format codeclimate > gl-code-quality-report.json
  artifacts:
    reports:
      codequality: gl-code-quality-report.json

Incremental analysis

Only check files changed since a git ref:

fallow dead-code --changed-since main
fallow dead-code --changed-since HEAD~5

This is useful in CI to only report new issues in a pull request.

$ fallow dead-code --changed-since main

● Unused exports (2)
  src/features/savings/hooks/usePotGroups.ts
    :8  usePotGroupTotals
  src/server/jobs/queue.ts
    :276 getDeadLetterJobs
  Exported symbols with zero references — https://docs.fallow.tools/explanations/dead-code#unused-exports

✗ 2 issues (0.04s)

Baseline comparison

Adopt fallow incrementally by saving a baseline of existing issues:

# Save current issues as baseline
fallow dead-code --save-baseline

# Only fail on new issues (compared to baseline)
fallow dead-code --baseline

Debugging

Trace why an export is or isn’t considered used:

fallow dead-code --trace src/utils.ts:formatDate
fallow dead-code --trace-file src/utils.ts
fallow dead-code --trace-dependency lodash

How it works

Fallow uses syntactic analysis with scope-aware binding resolution via Oxc. No TypeScript compiler, no type information. That’s what makes it fast. The graph-based approach guarantees completeness regardless of project size.

Fallow works best with projects using isolatedModules: true (required for esbuild, swc, and Vite). oxc_semantic scope analysis detects unused import bindings (imports where the bound name is never read), but legacy tsc-only projects without isolatedModules may still see edge cases with type-only imports.

Script binary analysis

Fallow parses package.json scripts to detect CLI tool usage. This reduces false positives in unused dependency detection. When you have a script like "lint": "eslint src/", fallow recognizes that eslint is a binary provided by the eslint package and marks it as used. How it works:

Binary name to package name mapping: Script commands like tsc, vitest, or next are mapped back to their parent packages (typescript, vitest, next). These packages won’t be reported as unused even when they’re never import-ed in source code.
--config arguments as entry points: When a script references a config file (e.g., jest --config jest.e2e.config.ts), fallow treats that config file as an entry point. Config files won’t be flagged as unused.
File path arguments: Direct file references in scripts (e.g., node scripts/seed.js) are also recognized as entry points.
Env wrappers and package manager runners: Commands prefixed with cross-env, npx, pnpx, yarn dlx, or node -r are unwrapped to find the actual tool binary.

{
  "scripts": {
    "build": "tsc && vite build",
    "test": "vitest --config vitest.config.ts",
    "lint": "cross-env NODE_ENV=production eslint src/"
  }
}

In this example, fallow detects typescript, vite, vitest, and eslint as used dependencies, and vitest.config.ts as an entry point.

Infrastructure entry points

Fallow scans infrastructure config files for source file references and treats them as entry points. Worker processes, migration scripts, and other infrastructure-defined files won’t be reported as unused. Supported files:

File type	What fallow extracts
Dockerfiles (`Dockerfile`, `Dockerfile.`, `.Dockerfile`)	`RUN node`, `CMD`, `ENTRYPOINT`, esbuild invocations
Procfiles	Process definitions (e.g., `worker: node dist/worker.js`)
fly.toml / *fly..toml**	`release_command` and process definitions
CI pipelines (`.gitlab-ci.yml`, `.github/workflows/*.yml`)	`npx` and binary invocations in CI steps

Fallow searches the project root and common subdirectories (config/, docker/, deploy/) for these files.

# Fallow detects scripts/migrate.ts and src/worker.ts as entry points
FROM node:20
RUN node scripts/migrate.ts
CMD ["node", "src/worker.ts"]

Dynamic import resolution

Fallow resolves dynamic imports that use patterns rather than static strings. When you write import(\./locales/$.json`)`, the import target isn’t known at analysis time. Fallow converts these patterns into glob expressions and matches them against discovered files. Supported patterns:

Pattern	Example	Resolved as
Template literals	import(`./icons/${name}.svg`)	`./icons/*.svg`
String concatenation	`import("./routes/" + path)`	`./routes/*`
`import.meta.glob`	`import.meta.glob("./modules/*.ts")`	`./modules/*.ts`
`require.context`	`require.context("./themes", true, /\.css$/)`	`./themes/*/.css`

Matched files are marked as reachable in the module graph, so they won’t be reported as unused. Useful for locale files, icon sets, route modules, and other convention-based directory structures.

Dynamic imports with fully runtime-computed paths (e.g., import(userInput)) cannot be resolved statically. Use entry in your config to mark those directories as entry points.

Re-export chain resolution

Fallow resolves export * chains through multiple levels of barrel files with cycle detection.

// utils/math.ts
export const add = (a: number, b: number) => a + b;

// utils/index.ts (barrel)
export * from './math';

// src/index.ts (barrel)
export * from './utils';

// app.ts
import { add } from './src';

In this example, fallow traces the import of add in app.ts through src/index.ts and utils/index.ts back to utils/math.ts. The add export is correctly marked as used across the entire chain. Resolution handles:

Multi-level chains: Any depth of export * re-exports is followed until the original declaration is found.
Cycle detection: Circular re-export chains (e.g., a re-exports from b, b re-exports from a) are detected and handled gracefully.
Mixed re-exports: Named re-exports (export { foo } from './bar') and namespace re-exports (export * from './bar') are both tracked.

Namespace import narrowing

When a file uses import * as ns from './module', fallow narrows which exports are actually consumed by scanning for member accesses (ns.foo, ns.bar) and destructuring patterns (const { foo, bar } = ns) in the importing file.

import * as utils from './utils';

// Only foo and bar are marked as used. baz remains unused
const { foo } = utils;
utils.bar();

Works with static imports, dynamic imports (const mod = await import('./x')), and require (const mod = require('./x')). Fallow also uses oxc_semantic scope analysis to detect imports where the binding is never read. An import { foo } from './utils' where foo is never referenced in the file does not count as a reference to the foo export. This improves unused-export detection precision.

Whole-object consumption patterns like Object.values(ns), { ...ns }, for (const k in ns), and rest destructuring (const { a, ...rest } = ns) conservatively mark all exports as used. Fallow can’t determine which specific members are accessed in these cases.

Class member detection

Fallow detects unused public class members (methods and properties) that are never referenced outside their defining class. Unlike simple text matching, fallow understands class inheritance, decorators, and framework conventions.

class OrderService {
  // Used: called in checkout.ts
  async createOrder(items: Item[]) { /* ... */ }
  
  // Unused: never called outside this class
  private validateItems(items: Item[]) { /* ... */ }
  
  // Excluded: decorator indicates runtime wiring
  @Post('/orders')
  handleCreateOrder() { /* ... */ }
}

What fallow handles automatically:

Inheritance: A method defined on a parent class and called via the parent type credits the child’s override as used
Decorators: Any decorated member is excluded from detection. Decorators like @Get(), @Column(), @Injectable() indicate runtime wiring
Framework lifecycle methods: componentDidMount, ngOnInit, connectedCallback, and other framework lifecycle methods are never flagged
Whole-object patterns: Object.values(instance), Object.keys(), spread operators, and for..in loops conservatively mark all members as used

Class member detection works via syntactic analysis, without invoking the TypeScript compiler. This means fallow tracks member access through the import graph, not through type resolution.

CSS and SCSS tracking

Fallow tracks CSS and SCSS imports using dedicated AST-based extraction. SCSS @use, @forward, and partial imports (_prefix files) are resolved accurately. CSS Module class names are extracted as named exports and tracked through styles.className member accesses. See CSS, SCSS, and Tailwind analysis for full details.

Entry-point partial unused exports

When a file is an entry point (matched by a plugin or the entry config), fallow traditionally marks all its exports as used. Starting in v2.15.0, fallow can detect partially unused exports in entry-point files: exports that exist in an entry file but are never imported by any other module in the project. This is especially useful for framework convention files (Next.js pages, SvelteKit routes) where the framework consumes specific named exports (like default, loader, or getStaticProps) but the file may also export helper functions that nothing uses.

Entry-point files are still considered used (never reported as unused files), but individual exports within them that have zero references are now reported as unused exports.

Cross-reference with duplication

Running fallow dead-code --include-dupes cross-references dead code findings with code duplication analysis. Clone instances in unused files, or overlapping with unused exports, are flagged as combined high-priority findings.

fallow dead-code --include-dupes

Use --include-dupes to prioritize cleanup: if a block of code is both duplicated and unused, removing it eliminates dead code and reduces duplication at the same time. What the cross-reference finds:

Clone instances in unused files: If a file is unreachable from entry points and contains duplicated code, the duplication finding is elevated.
Clone instances overlapping unused exports: If an unused export contains code that is duplicated elsewhere, both findings are reported together.

Use --include-dupes in CI to surface code that is both unused and duplicated.

Circular dependency benchmarks

Fallow detects dependency cycles during module graph construction at no extra cost. Standalone tools like madge and dpdm build their own graph from scratch.

Project	Files	fallow	madge	dpdm	vs madge	vs dpdm
zod	174	17ms	540ms	190ms	32x	11x
preact	244	19ms	298ms	132ms	16x	7x
fastify	286	20ms	165ms	132ms	8x	7x
vue/core	522	59ms	175ms	143ms	3x	2x
TanStack/query	901	134ms	168ms	137ms	1.3x	1.0x

3-32x faster than madge, 2-11x faster than dpdm on small-to-medium projects. Fallow uses 5-7x less memory by reusing the module graph already built for dead code analysis.

CLI: dead-code

Full reference for the fallow dead-code command and its flags.

Rules & Severity

Control which issue types are errors, warnings, or disabled.

Auto-fix

Automatically remove the dead code fallow finds.

Getting Started

Analysis

Configuration

Integrations

Explanations

Frameworks

Migration

Dead code analysis

Issue types

Filtering by issue type

Output formats

Incremental analysis

Baseline comparison

Debugging

How it works

Script binary analysis

Infrastructure entry points

Dynamic import resolution

Re-export chain resolution

Namespace import narrowing

Class member detection

CSS and SCSS tracking

Entry-point partial unused exports

Cross-reference with duplication

Circular dependency benchmarks

See also

CLI: dead-code

Rules & Severity

Auto-fix

Getting Started

Analysis

Configuration

Integrations

Explanations

Frameworks

Migration

Documentation Index

​Issue types

​Filtering by issue type

​Output formats

​Incremental analysis

​Baseline comparison

​Debugging

​How it works

​Script binary analysis

​Infrastructure entry points

​Dynamic import resolution

​Re-export chain resolution

​Namespace import narrowing

​Class member detection

​CSS and SCSS tracking

​Entry-point partial unused exports

​Cross-reference with duplication

​Circular dependency benchmarks

​See also

CLI: dead-code

Rules & Severity

Auto-fix

Issue types

Filtering by issue type

Output formats

Incremental analysis

Baseline comparison

Debugging

How it works

Script binary analysis

Infrastructure entry points

Dynamic import resolution

Re-export chain resolution

Namespace import narrowing

Class member detection

CSS and SCSS tracking

Entry-point partial unused exports

Cross-reference with duplication

Circular dependency benchmarks

See also