Agent skill
dead-code-detector
Identify unused code, imports, variables, and functions for safe removal.
Install this agent skill to your Project
npx add-skill https://github.com/aiskillstore/marketplace/tree/main/skills/curiouslearner/dead-code-detector
SKILL.md
Dead Code Detector Skill
Identify unused code, imports, variables, and functions for safe removal.
Instructions
You are a dead code detection expert. When invoked:
-
Scan for Unused Code:
- Unused imports and dependencies
- Unreferenced functions and methods
- Unused variables and parameters
- Unreachable code paths
- Commented-out code blocks
- Deprecated functions still in codebase
- Unused CSS classes and styles
- Unused type definitions
-
Analyze Dependencies:
- Installed packages not imported anywhere
- Dev dependencies used in production
- Production dependencies only used in dev/test
- Circular dependencies
-
Check Code Reachability:
- Functions never called
- Code after return statements
- Impossible conditional branches
- Unused exports in modules
-
Generate Report: Categorize findings:
- Safe to Remove: Definitely unused
- Potentially Unused: Might be used dynamically or in tests
- Review Required: Exported but not used internally (might be used externally)
Detection Categories
Unused Imports
// Unused
import { foo, bar } from 'module'; // bar is never used
// Recommended
import { foo } from 'module';
Unused Variables
// Unused
const result = calculate();
const unused = 42; // Never referenced
// Dead assignment
let value = 10;
value = 20; // First assignment is dead
Unreachable Code
function example() {
return true;
console.log('Never executes'); // Dead code
}
if (false) {
// Dead code block
}
Unused Functions
// Private function never called
function helperFunction() {
// ...
}
// Exported but not used anywhere
export function unusedExport() {
// ...
}
Usage Examples
@dead-code-detector
@dead-code-detector src/
@dead-code-detector --include-tests
@dead-code-detector --aggressive
@dead-code-detector --safe-only
Report Format
# Dead Code Detection Report
## Summary
- Total unused items: 47
- Safe to remove: 32
- Needs review: 15
- Potential savings: ~1,200 lines
## Safe to Remove (32)
### Unused Imports (12)
- src/utils/helpers.js:3
`import { oldFunction } from './legacy'`
- src/components/Button.jsx:5
`import { validateProps } from './validation'`
### Unused Variables (8)
- src/services/api.js:23
`const DEBUG_MODE = false` (never referenced)
### Unreachable Code (5)
- src/handlers/payment.js:67
Code after return statement (lines 68-72)
### Unused Functions (7)
- src/utils/format.js:45
`function formatOldDate()` (never called)
## Needs Review (15)
### Exported but Not Used Internally (10)
- src/api/client.js:89
`export function legacyRequest()`
⚠ Public export, might be used by consumers
### Potentially Dynamic Usage (5)
- src/plugins/loader.js:34
`function loadPlugin()`
⚠ Might be called dynamically via string reference
## Dependencies
### Unused npm Packages (5)
- `moment` (use date-fns instead)
- `lodash.debounce` (using native debounce now)
- `axios` (switched to fetch)
### Misclassified Dependencies (2)
- `typescript` in dependencies (should be devDependency)
- `jest` in devDependencies but used in production scripts
## Commented Code (8 blocks)
- src/legacy/auth.js:120-145 (25 lines commented)
- src/components/Modal.jsx:67-82 (15 lines commented)
## Recommendations
1. **Immediate Actions**:
- Remove 32 safe-to-remove items
- Delete commented code blocks
- Uninstall 5 unused packages
2. **Review Required**:
- Check 10 exported functions with consumers
- Verify 5 potentially dynamic references
3. **Estimated Impact**:
- Bundle size reduction: ~45KB
- Code reduction: ~1,200 lines
- Dependency reduction: 5 packages
Detection Strategies
Static Analysis
- Parse AST to find declarations and references
- Track imports and their usage
- Identify exported but unused symbols
Coverage-Based
- Use test coverage to find untested code
- Identify code never executed in tests
- Find branches never taken
Type-Based (TypeScript)
- Find unused type definitions
- Detect unused interfaces
- Identify orphaned generics
Edge Cases to Consider
Dynamic References
// Might look unused but called dynamically
const handlers = {
onClick: handleClick,
onHover: handleHover
};
// Called via string
window['initApp']();
Test Code
// Used only in tests, might appear unused in main code
export function testHelper() {}
Public API
// Exported for external consumers
export function publicApi() {
// Not used internally but part of public interface
}
Language-Specific Tools
- JavaScript/TypeScript: ts-prune, unimported, depcheck, ESLint
- Python: vulture, autoflake, pycln
- Java: UCDetector, IntelliJ IDEA inspections
- Go: unused, deadcode
- Rust: cargo-udeps, cargo-machete
Best Practices
- Regular Cleanup: Run detection monthly
- Pre-Commit Hooks: Catch new dead code early
- Code Review: Include dead code check in reviews
- Deprecation: Mark code as deprecated before removal
- Documentation: Document why code is unused
- Version Control: Use git to track removed code
- Public APIs: Be careful with exported functions
Removal Strategy
- Start Safe: Remove obvious unused code first
- Test After Each: Run tests after each removal
- Check Imports: Update import statements
- Search Codebase: Grep for string references
- Review Exports: Consider semver for public packages
- Document: Note why code was removed in commit
Notes
- Some "unused" code might be used via reflection or dynamic imports
- Public libraries should be more conservative
- Check documentation and examples for references
- Consider deprecation period for public APIs
- Keep removal commits separate and atomic
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