Claude Prompts for Coding: Debug, Refactor, Test
Claude handles most common coding tasks well — debugging, refactoring, writing tests, code review, documentation, and explaining unfamiliar code. This page collects copy-ready prompt templates for each task, organized by use case.
See our Claude for Coding guide for a broader overview of how to use Claude in development workflows, and our Claude Prompts hub for general prompting tips.
Debugging Prompts
Basic Debugging
Here is an error I'm getting:
[paste error message or stack trace]
Here is the relevant code:
[paste code]
What is causing this error and how do I fix it?Unexpected Behavior (No Error)
This code runs without errors but produces unexpected output. Expected: [what should happen]. Actual: [what happens instead].
[paste code]
What might be causing the wrong output and how should I fix it?Intermittent Bug
I have a bug that happens intermittently — not every time the code runs. Here are the conditions when it tends to appear: [describe]. Language/framework: [stack]. Here is the code:
[paste code]
What might be causing this and how would I debug it systematically?Refactoring Prompts
General Refactor
Refactor this code to improve readability and reduce repetition. Keep the same behavior. Language: [language]. Framework: [framework].
[paste code]Extract a Function
Extract the [describe logic] in this code into a separate, reusable function. Name it [suggested name or "something descriptive"]. Keep the rest of the code unchanged.
[paste code]Apply a Design Pattern
Refactor this code to use the [pattern name: factory / observer / singleton / strategy / etc.] pattern. Explain what changes you made and why the pattern applies here.
[paste code]Reduce Complexity
This function has too many responsibilities. Suggest how to split it into smaller functions, each with a single responsibility. Show the refactored version.
[paste function]Writing Tests Prompts
Write Unit Tests
Write unit tests for this function using [pytest / Jest / RSpec / JUnit / etc.]. Cover: normal cases, edge cases, and at least one error/exception case.
[paste function]Test for Edge Cases
What edge cases should I test for this function? List the cases and then write tests for each one.
[paste function]Write Integration Tests
Write integration tests for this module. The module interacts with [describe what it connects to: API / database / file system]. Use [testing framework]. Focus on testing the interaction points, not just internal logic.
[paste code]Generate Test Data
Generate test data for this schema/function. Include examples for: valid inputs, invalid inputs, boundary values, and empty/null cases.
[paste schema or function signature]Code Review Prompts
General Code Review
Review this code for: bugs, potential security issues, performance problems, and readability. Be specific about any issues you find — include line numbers or function names. Language: [language].
[paste code]Security Review
Review this code specifically for security issues. Look for: injection vulnerabilities, improper input validation, insecure defaults, authentication or authorization gaps, and any other security concerns.
[paste code]Performance Review
Review this code for performance issues. Identify any unnecessary loops, redundant database queries, memory leaks, or inefficient algorithms. Suggest improvements.
[paste code]Documentation Prompts
Add Docstrings
Add docstrings to all public functions in this file. Use [Google style / NumPy style / JSDoc / etc.] format. Include: description, parameters, return values, and any exceptions raised.
[paste code]Write a README
Write a README.md for this project. Include: what it does, how to install it, how to use it (with an example), and any configuration options. Language: [language]. Framework: [framework].
[paste relevant code or description]Explain Code for a Handoff
Write an explanation of this codebase section suitable for a developer who is taking it over. Cover: what it does, how it's structured, the key functions and their roles, and any non-obvious design decisions.
[paste code or describe the section]Code Explanation Prompts
Explain What Code Does
Explain what this code does, step by step. Assume I understand the programming language but am unfamiliar with this specific logic.
[paste code]Explain a Specific Function
Explain what this function does, what inputs it takes, what it returns, and what side effects it has (if any).
[paste function]Explain an Error Message
What does this error message mean? What are the most common causes, and how would I typically fix each one?
[paste error message]Architecture and Planning Prompts
Plan a Feature
I need to implement [feature description]. Tech stack: [stack]. Existing system: [brief description]. Outline the implementation steps, key components to build, and any potential pitfalls to watch for.Evaluate Two Approaches
I'm deciding between [approach A] and [approach B] for [problem]. Trade-offs I'm considering: [list]. My priority is [performance / maintainability / speed of implementation / etc.]. Which approach would you recommend and why?Database Schema Design
Design a database schema for [what it stores]. Requirements: [list key requirements]. Database: [PostgreSQL / MySQL / SQLite / MongoDB / etc.]. Show the tables/collections and their fields with types. Flag any design decisions I should consider carefully.Tips for Coding Prompts
- Always specify the language and framework: “Fix this code” is less useful than “Fix this TypeScript function using React hooks.”
- Include the full error when debugging: The stack trace often contains the key clue.
- Say what must not change: When refactoring, specify what behavior, naming, or API must stay the same.
- Ask for explanations: Adding “Explain what you changed and why” to a refactor or debug request gives you better output to learn from.
- Test all output: Claude cannot run your code. Always test before deploying. See our Claude for Coding guide for safe usage notes.