Use Claude Code to fix the bug you can't find

The problem. Something’s broken, users have mentioned it, and you’ve spent an hour staring at the code without finding it. You’re a founder, not a debugging specialist, and the bug doesn’t care.

The play. Point Claude Code at the actual codebase and the actual symptom, and let it investigate — reading real files, checking real logic — instead of asking a chat window to guess from your description of the problem.

Setup (5 min). Open Claude Code (see what Claude Code actually is if you’re new to it) in the project folder. Gather whatever you actually have: the error message, steps to reproduce if you know them, when it started happening.

The prompt:

Here's the bug: [describe exactly what's happening, any error message, and
how to reproduce it if you know].

Investigate the actual code to find the root cause — don't guess without
checking. Read the relevant files, trace the logic, and tell me:
1. What's actually causing this, with the specific file and line
2. Why it happens (the actual mechanism, not just "there's a bug here")
3. A proposed fix — but don't apply it yet, show me the diff first

If you can't find the cause with high confidence, say so and tell me what
additional information would help, rather than proposing a guessed fix.

What you get. A specific, file-and-line diagnosis instead of a plausible-sounding guess — and a diff you review before anything changes, so you’re not trusting a fix you don’t understand.

What to watch for.

• The “don’t guess without checking” instruction matters. Without it, a model can produce a confident-sounding fix for the wrong cause.
• Review the diff yourself before accepting it, especially for anything touching real user data or payments — a fix that resolves the symptom isn’t the same as one that resolves the actual cause.

Make it repeatable. Once fixed, ask Claude Code to write a short note in DECISIONS.md about what broke and why — future-you debugging something similar in month four will thank present-you. Pair this with the PR-review playbook before you merge the fix.