Strict code review that ignores style
codingReviews a diff for correctness, edge cases, and regressions — and refuses to comment on formatting.
Refactor without changing behavior
Extracts or restructures code while proving the public behavior stays identical.
When to use it
When a function has grown past reading size but is covered by tests you cannot afford to rewrite.
The prompt
Copy into your assistant
Refactor the code below without changing its observable behavior.
Constraints:
- Public signatures stay identical.
- No new dependencies.
- No behavior changes, including error types, ordering, and side effects.
- If you cannot preserve behavior with confidence, stop and say which line makes it unsafe.
Before writing code, list:
1. The observable contract (inputs, outputs, errors, side effects).
2. Which existing tests cover it, if any are shown.
3. The single riskiest line for behavior preservation.
Then output the refactored code, followed by a one-paragraph note on what a reviewer should check.
Code:
<code>What to change
If there are no tests, say so explicitly — the model will then write thin characterisation checks first instead of refactoring blind.
Why it works
Asking for the contract before the code forces the model to read the function instead of pattern-matching it. The 'riskiest line' question surfaces exactly where a silent regression would hide.
More coding prompts
- Turn a bug report into a failing testWrites the failing test first, then the fix, and refuses to skip the reproduction.
- Explain unfamiliar code before touching itProduces a map of responsibilities, data flow, and the parts that look dangerous to change.
- Question to SQL, with the assumptions spelled outTurns a business question into a query plus the schema assumptions it made.
Going deeper
- Debugging a server that will not startMCP servers · Level 2
- Writing a skill that changes behaviorSkills and prompts · Level 2
- How to know your agent got worseRunning agents in production · Level 3