Claude for refactoring code, done properly.

Legacy code works but is unmaintainable. New developers can't understand it, adding features creates bugs, and nobody wants to touch it. But a rewrite is too risky.

Three reasons this actually lands.

The prompt, the codes, the fit. Each one on its own is a nice-to-have. Together, they change the workflow.

Copy this, replace the placeholders, ship.

Refactor this code for maintainability.

Language: [LANGUAGE]
What it does: [BUSINESS LOGIC EXPLANATION]
Why it needs refactoring: [WHAT'S PAINFUL — hard to modify? slow? untestable?]
Constraints: [MUST MAINTAIN BACKWARD COMPATIBILITY? API CONTRACTS?]

```[language]
[PASTE CODE]
```

Rules:
1. Show the refactoring in steps (not one giant rewrite)
2. Each step should be a safe, testable change
3. Preserve external behavior — this is refactoring, not redesign
4. Name the patterns you're applying (Extract Method, Replace Conditional with Polymorphism, etc.)
5. Explain each decision — why this structure is better for future changes
6. Flag anything that needs tests before refactoring (safety net)

Replace the [BRACKETED] placeholders with your context.

Stack these prefixes for compound gains.

Prepend one or more of these to the prompt above. Each code is documented on its own page with before and after examples.

Every prompt, once.

The Cheat Sheet is every tested code, with a before and an after.