# refactor

Walks the agent through six refactoring phases: code analysis, test check, code smell hunt, plan, incremental edits and review.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · ★ 45153
- Author: luongnv89
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/luongnv89/claude-howto/tree/HEAD/03-skills/refactor/SKILL.md
- Updated: 2026-10-20
- HTML: https://affpapa.org/en/nevibecode/skills/luongnv89-refactor

## What it does

The skill follows Martin Fowler's method from Refactoring: Improving the Design of Existing Code (2nd Edition). External behavior stays the same; only the internal structure changes. Work moves in small steps, and the agent asks for your approval at each phase before continuing.

Six phases sit inside. First the agent clarifies scope, goals and constraints, then reads the target code and its dependencies. Next it checks whether tests exist and pass, using commands like `npm test`, `pytest -v` or `mvn test`. Then it hunts code smells against a catalog: long methods, duplicated code, large classes, long parameter lists, dead code. Each one gets a severity and a priority. The plan that follows maps every smell to a refactoring technique, with micro-steps, risks and a rollback path. Implementation starts with the cheap, low-risk edits.

One limit is built into the process itself: if tests fail, work stops until they are fixed. With no tests at all, the skill offers three options, write them first, add them as you go, or proceed without a safety net and accept the risk. A helper script, `scripts/detect-smells.py`, can scan a file, though the smell review works fine by hand.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add luongnv89/claude-howto --skill refactor -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/refactor/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/refactor/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add luongnv89/claude-howto --skill refactor -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/refactor/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add luongnv89/claude-howto --skill refactor -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/refactor/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install luongnv89/claude-howto refactor
```

2. **Manually: put the files in place**
- File: `.github/skills/refactor/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add luongnv89/claude-howto --skill refactor -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/luongnv89/claude-howto --path 03-skills/refactor
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/refactor/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add luongnv89/claude-howto --skill refactor -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/luongnv89/claude-howto/tree/HEAD/03-skills/refactor/SKILL.md

## When to use it
- map a legacy module and decide where edits should start
- spot duplication and long methods in unfamiliar code
- draft a refactoring plan with steps and a rollback path
- check whether a section is covered by tests before touching it
- strip dead code and speculative abstractions

## Example prompts
- refactor the payments module, show me the plan first
- find code smells in `src/orders.py` and rank them
- check the tests before refactoring the UserService class

## Source text · SKILL.md · MIT

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BEGIN THIRD-PARTY FILE 2a4bbf43b4558b10
````text
---
name: refactor
description: Systematic code refactoring based on Martin Fowler's methodology. Use when users ask to refactor code, improve code structure, reduce technical debt, clean up legacy code, eliminate code smells, or improve code maintainability. This skill guides through a phased approach with research, planning, and safe incremental implementation.
---

# Code Refactoring Skill

A systematic approach to refactoring code based on Martin Fowler's *Refactoring: Improving the Design of Existing Code* (2nd Edition). This skill emphasizes safe, incremental changes backed by tests.

> "Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure." — Martin Fowler

## Core Principles

1. **Behavior Preservation**: External behavior must remain unchanged
2. **Small Steps**: Make tiny, testable changes
3. **Test-Driven**: Tests are the safety net
4. **Continuous**: Refactoring is ongoing, not a one-time event
5. **Collaborative**: User approval required at each phase

## Workflow Overview

```
Phase 1: Research & Analysis
    ↓
Phase 2: Test Coverage Assessment
    ↓
Phase 3: Code Smell Identification
    ↓
Phase 4: Refactoring Plan Creation
    ↓
Phase 5: Incremental Implementation
    ↓
Phase 6: Review & Iteration
```

---

## Phase 1: Research & Analysis

### Objectives
- Understand the codebase structure and purpose
- Identify the scope of refactoring
- Gather context about business requirements

### Questions to Ask User
Before starting, clarify:

1. **Scope**: Which files/modules/functions need refactoring?
2. **Goals**: What problems are you trying to solve? (readability, performance, maintainability)
3. **Constraints**: Are there any areas that should NOT be changed?
4. **Timeline pressure**: Is this blocking other work?
5. **Test status**: Do tests exist? Are they passing?

### Actions
- [ ] Read and understand the target code
- [ ] Identify dependencies and integrations
- [ ] Document current architecture
- [ ] Note any existing technical debt markers (TODOs, FIXMEs)

### Output
Present findings to user:
- Code structure summary
- Identified problem areas
- Initial recommendations
- **Request approval to proceed**

---

## Phase 2: Test Coverage Assessment

### Why Tests Matter
> "Refactoring without tests is like driving without a seatbelt." — Martin Fowler

Tests are the **key enabler** of safe refactoring. Without them, you risk introducing bugs.

### Assessment Steps

1. **Check for existing tests**
   ```bash
   # Look for test files
   find . -name "*test*" -o -name "*spec*" | head -20
   ```
````
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