Systematic Debugging

Never guess at fixes. Find the root cause first.

Phase 1: Understand the Error

• Read the full error message
• Note the exact file, line, error type
• Reproduce the error reliably
• Write: 'The error is: [exact error] at [location] when [trigger].'

Phase 2: Hypothesize

Generate at least 2 hypotheses. For each: what evidence supports it? What would disprove it?

Phase 3: Test Hypotheses

Test each hypothesis with the minimum change to confirm or deny it.

• Add a log line, not a fix
• Test one variable at a time

Phase 4: Fix and Verify

1. Write the fix
2. Verify the original error is gone
3. Verify no new errors
4. Add a test that would have caught this bug