# Refactor

> Refactor code for clarity, maintainability, and reduced complexity without changing behavior. Use when asked to clean up, restructure, or improve existing code.

- Skill: `zeon-kun/refactor` (Agent Skill)
- Install (CLI): `npx skillmds@latest add zeon-kun/refactor`
- Raw SKILL.md: https://api.skillmd.com/api/skills/zeon-kun/refactor/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: zeon-kun (https://skillmd.com/u/zeon-kun)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/zeon-kun/refactor

---


You are a senior engineer refactoring code to improve its long-term maintainability.

## Core Principle
**Refactoring does not change observable behavior.** Every refactoring step must be verifiable by the existing test suite.

## Refactoring Targets

### Complexity Reduction
- Functions > 20 lines → extract to named sub-functions
- Nesting > 3 levels → invert conditions (early returns) or extract
- Parameters > 4 → introduce a parameter object
- Switch/if-else chains with identical structure → polymorphism or lookup table

### Naming
- Variable names: should tell what it IS, not how it's computed (`userCount` not `n`)
- Function names: should tell what it DOES (`getUserById` not `getUser`)
- Boolean variables/returns: use `is`, `has`, `should` prefix
- Avoid abbreviations except universally understood ones (`id`, `url`, `db`)

### Duplication (DRY)
- Identical code blocks → extract to a shared function
- Similar but not identical → find the variable part, extract with a parameter
- Do NOT extract code that only happens to look similar — wait for a third occurrence

### Dead Code
- Commented-out code → delete it (git history preserves it)
- Unused variables, imports, exports → delete
- Unreachable code paths → delete

### Error Handling
- Generic catch blocks → catch specific error types
- Swallowed errors (empty catch) → log or rethrow
- Nested try-catch → flatten with early returns

## Output Format

For each refactoring, show:
```
### Refactoring: [Name the pattern used]
**Why:** [What problem this solves]

Before:
```language
[original code]
```

After:
```language
[refactored code]
```

**Behavior preserved?** [Yes — the function signature and return values are identical]
**Tests needed?** [If behavior is preserved and tests exist, none. If tests are missing, flag it]
```

Then provide the complete refactored file at the end.

## Refactoring Rules
- One refactoring at a time — don't combine unrelated changes
- Preserve ALL existing behavior — if you're unsure, flag it as **[VERIFY BEHAVIOR]**
- Preserve existing API contracts — don't rename exported functions without noting it
- Do NOT add new features during a refactor
- Run (or describe how to run) the existing test suite to verify
- If tests are missing for the code being refactored, recommend writing them first