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Debugging with Claude Code

Claude Code is an effective debugging partner. It can read stack traces, trace logic through your codebase, form hypotheses, and apply fixes — all within your terminal. This guide covers strategies for getting the best debugging results.

Start with Context

The most important thing you can give Claude when debugging is a clear description of the problem. Include:

  • What you expected to happen
  • What actually happened (error message, wrong output, crash)
  • Steps to reproduce if the bug is not obvious

```bash

Good: specific and actionable

claude "The /api/users endpoint returns 500 when the email field contains a plus sign. Here's the error from the logs: [paste error]"

Less effective: vague

claude "The API is broken" ```

Debugging Strategies

Paste the Error

The simplest approach — paste the full stack trace or error message directly into your prompt. Claude will read the referenced files, identify the root cause, and suggest a fix.

```bash claude "I'm getting this error when running tests:

TypeError: Cannot read properties of undefined (reading 'map') at UserList (src/components/UserList.tsx:14:22) at renderWithHooks (node_modules/react-dom/...)

Fix this bug." ```

Let Claude Investigate

For bugs without a clear error message, describe the symptom and let Claude explore:

bash claude "The search feature returns duplicate results when the query contains uppercase letters. Investigate and fix."

Claude will read the relevant code, trace the logic, and identify where the issue occurs. This works well because Claude can follow code paths across multiple files.

Use Logs and Output

Pipe log output directly into Claude for analysis:

bash cat logs/error.log | claude "Analyze these logs and identify the root cause of the failures"

Or ask Claude to add logging to narrow down a problem:

bash claude "Add debug logging to the payment processing pipeline so we can trace where the order total becomes negative"

Reproduce First

For intermittent bugs, ask Claude to write a reproduction:

bash claude "Users report that the cart sometimes shows stale prices after a product update. Write a test that reproduces this race condition."

A failing test makes the bug concrete and verifiable, and gives Claude a clear target for the fix.

Debugging Workflows

The Fix-and-Verify Loop

The most reliable debugging workflow:

  1. Describe the bug with as much context as possible
  2. Let Claude investigate the codebase and propose a fix
  3. Ask Claude to run the tests to verify the fix works
  4. Review the changes before committing

bash claude "Fix the bug where deleted users still appear in search results. Run the tests after fixing to make sure nothing else breaks."

Bisecting with Claude

When you know a bug was introduced recently but not which commit:

bash claude "The login page broke sometime in the last week. Check the recent commits that touched auth-related files and identify which change introduced the regression."

Debugging Performance Issues

Ask Claude to profile and analyze:

bash claude "The dashboard page takes 8 seconds to load. Profile the API calls and database queries to find the bottleneck."

Claude can add timing instrumentation, analyze query plans, and suggest optimizations.

Working with Stack Traces

Claude excels at reading stack traces. For best results:

  • Paste the complete trace, not just the error line
  • Include the language and framework if not obvious from the trace
  • Mention what triggered the error (which action, endpoint, or test)

Debugging in Different Contexts

Frontend Bugs

For UI issues, describe what you see:

bash claude "The modal closes immediately after opening on mobile Safari. It works fine on Chrome desktop. The modal component is in src/components/Modal.tsx."

API and Backend Bugs

Include the request, response, and expected behavior:

bash claude "POST /api/orders with this payload returns 422 but should succeed: {\"items\": [{\"id\": 1, \"qty\": 2}]}. The validation error says 'price is required' but price should come from the database."

Database Issues

Provide the query or migration context:

bash claude "This query returns wrong results after we added the soft-delete column. Fix the query to exclude deleted records: SELECT * FROM orders WHERE user_id = $1"

Tips for Effective Debugging

  • One bug at a time. Do not ask Claude to fix multiple unrelated bugs in one prompt. Start a new conversation or use /clear between bugs.
  • Share the error, not your guess. Let Claude form its own hypothesis from the evidence. Saying "I think the bug is in X" can bias the investigation.
  • Ask for tests. After a fix, ask Claude to add a test that would catch the same bug if it regresses.
  • Use headless mode for CI debugging. Pipe CI logs into Claude to diagnose build failures: cat ci-output.log | claude -p "Why did this build fail?"
  • Check related code. Ask Claude to verify that similar patterns elsewhere do not have the same bug.

See Also