---
name: refactoring
description: Governs code refactoring, code cleanup, deduplication, extract function, technical debt, dead code pruning, and architectural restructuring without regressions.
title: refactoring
canonical_url: https://skilld.dev/gh/amanktyr/tailor/refactoring
last_updated: 2026-09-24T09:50:05.000Z
---

> **Skill from skilld.dev.** Follow the instructions below for this session. You do not need to install anything.
>
> If the user asked to install this Skill, run `npx skilld install amanktyr/tailor/refactoring`. Install writes the Skill files into the project, so every session loads them.

# Refactoring Skill

Activate this skill when restructuring existing code, eliminating duplicates, modernizing patterns, decomposing monolithic functions, or pruning dead code.

> **Refactoring Law:** *Refactoring improves the internal structure of software without altering its external observable behavior.*

---

## 1. Safety & Baseline Invariants

Before modifying any existing implementation:
1. **Verify Baseline Tests:** Run existing test suites (`npm test`, `pytest`, `cargo test`) and confirm that all tests pass before making any changes.
2. **Preserve Public API Contracts:** Never alter exported function signatures, route parameters, or database schemas without a documented deprecation plan and updating all internal call sites.
3. **Atomic, Incremental Changes:** Refactor in small, verifiable steps. Never attempt large-scale rewrites in a single unverified commit.

---

## 2. Standard Refactoring Patterns

### A. Extract Function / Helper
* **Problem:** Monolithic 200-line function with mixed levels of abstraction.
* **Solution:** Extract isolated operations into small, single-responsibility pure functions in `src/utils/` or `src/lib/`.

### B. Introduce Parameter Object
* **Problem:** Functions accepting 6+ positional arguments (`function createUser(name, email, age, role, status, plan)`).
* **Solution:** Replace with a typed configuration object (`interface CreateUserOptions`).

### C. Strangler Fig Pattern (For Legacy Subsystem Migration)
* **Problem:** Migrating a legacy service to a new architecture without risky downtime.
* **Solution:** Build the new implementation alongside the legacy service; route traffic incrementally through a facade until the old system is completely superseded, then prune the legacy code.

---

## 3. Duplicate Elimination & Dead Code Pruning

* Search for repeated logic blocks across components using the AST duplicate finder.
* Consolidate duplicate helpers into a shared utility, replace all call sites, and remove dead unused exports.
* Re-run all verification suites and confirm **0 regressions**.

---

## 4. Refactoring Anti-Patterns & Step-by-Step Checklist

### Anti-Pattern: Unsolicited Scope Expansion (Refactoring Creep)
```ts
// ❌ WRONG: When asked to fix a date bug, rewriting unrelated CSS, variable names, and helper functions
// Results in huge diffs, merge conflicts, and subtle regressions.
```
```ts
// ✅ CORRECT: Surgical, focused refactoring preserving existing contracts
// Only modify what is directly necessary to eliminate duplicate or dead code.
// Preserve all existing function signatures and behavior.
```

### Mandatory 4-Step Refactoring Checklist
1. **[ ] Pre-Flight Baseline:** Run existing tests (`npm test`) and confirm exit code 0 *before* making any changes.
2. **[ ] Call-Site Audit:** Grep all references to the target function/component to ensure no breaking changes across callers.
3. **[ ] Surgical Execution:** Apply the minimal structural transformation without altering runtime behavior or external outputs.
4. **[ ] Regression Confirmation:** Re-run targeted and full test suites to verify 0 regressions.