knip-dead-code

Knip Dead Code Detection

Knip is a comprehensive tool for finding unused code, dependencies, and exports in JavaScript and TypeScript projects. It helps maintain clean codebases and catch dead code before it accumulates.

Knip finds statically unreachable code. Reach for a different tool for unused CSS (PurgeCSS), runtime dead code paths, bundle-size trimming (bundler tree-shaking), or duplicate dependencies (npm-dedupe).

Core Expertise

What is Knip?

• Unused detection: Files, dependencies, exports, types, enum members
• Plugin system: Supports 80+ frameworks and tools
• Fast: Analyzes large codebases in seconds
• Actionable: Clear reports with file locations
• CI-ready: Exit codes for failing builds

Installation

# Project-local (recommended)
bun add --dev knip

# Verify installation
bunx knip --version

Basic Usage

# Run Knip (scans entire project)
bunx knip

# Show only unused dependencies
bunx knip --dependencies

# Show only unused exports
bunx knip --exports

# Show only unused files
bunx knip --files

# Production mode (only check production dependencies)
bunx knip --production

# Exclude specific issue types
bunx knip --exclude-exports-used-in-file

# Output JSON (for CI)
bunx knip --reporter json

# Debug mode (show configuration)
bunx knip --debug

Configuration

Auto-detection (Zero Config)

Knip automatically detects:

• Entry points (package.json main, exports, bin)
• Frameworks (Next.js, Vite, Remix, etc.)
• Test runners (Vitest, Jest, Playwright)
• Build tools (ESLint, TypeScript, PostCSS)

No configuration needed for standard projects.

knip.json (Explicit Configuration)

{
  "$schema": "https://unpkg.com/knip@latest/schema.json",
  "entry": ["src/index.ts", "src/cli.ts"],
  "project": ["src/**/*.ts"],
  "ignore": ["**/*.test.ts", "scripts/**"],
  "ignoreDependencies": ["@types/*"],
  "ignoreBinaries": ["npm-check-updates"]
}

knip.ts (TypeScript Configuration)

// knip.ts
import type { KnipConfig } from 'knip';

const config: KnipConfig = {
  entry: ['src/index.ts', 'src/cli.ts'],
  project: ['src/**/*.ts', 'scripts/**/*.ts'],
  ignore: ['**/*.test.ts', '**/*.spec.ts', 'tmp/**'],
  ignoreDependencies: [
    '@types/*', // Type definitions
    'typescript', // Always needed
  ],
  ignoreExportsUsedInFile: true,
  ignoreWorkspaces: ['packages/legacy/**'],
};

export default config;

Common Patterns

Check Only Unused Dependencies

# Fastest check - only dependencies
bunx knip --dependencies

# Exit with error if any unused dependencies
bunx knip --dependencies --max-issues 0

Use in CI to enforce strict dependency hygiene.

Check Only Exports (Library Development)

# Check for unused exports
bunx knip --exports

# Allow exports used in same file
bunx knip --exports --exclude-exports-used-in-file

Use for libraries to ensure clean public API.

Production vs Development Dependencies

# Check production code only
bunx knip --production

# Check everything (including dev dependencies)
bunx knip

Interpreting Results

Example Output

No unused files
No unused dependencies
2 unused exports

src/utils.ts:
  - calculateTax (line 42)
  - formatDate (line 58)

src/types.ts:
  - UserRole (line 12)

Issue Types

Type	Description	Action
Unused file	File not imported anywhere	Delete or add to entry points
Unused dependency	Package in package.json not used	Remove from dependencies
Unused export	Exported but never imported	Remove export or make private
Unused type	Type/interface exported but unused	Remove or make internal
Unused enum member	Enum member never referenced	Remove member
Duplicate export	Same export from multiple files	Consolidate exports

Agentic Optimizations

Context	Command
Quick scan	bunx knip
Dependencies only	bunx knip --dependencies
Exports only	bunx knip --exports
CI strict mode	bunx knip --max-issues 0
Production check	bunx knip --production
JSON output	bunx knip --reporter json
Debug config	bunx knip --debug
Changed files	bunx knip --changed --base main

Quick Reference

Flag	Description
--dependencies	Check only unused dependencies
--exports	Check only unused exports
--files	Check only unused files
--production	Production dependencies only
--max-issues N	Fail if more than N issues
--reporter json	JSON output for CI
--reporter compact	Compact output
--debug	Show configuration details
--changed	Check only changed files
--changed --base main	Changed files since main
--workspace NAME	Check specific workspace
--exclude-exports-used-in-file	Ignore same-file exports

For detailed examples, advanced patterns, and best practices, see REFERENCE.md.

References

• Official docs: https://knip.dev
• Configuration: https://knip.dev/reference/configuration
• Plugins: https://knip.dev/reference/plugins
• CLI reference: https://knip.dev/reference/cli
• FAQ: https://knip.dev/reference/faq