Debug

Debug Skill

Debugging Process

1. Reproduce

• Get the exact error message
• Find the minimal steps to trigger it
• Note the environment (Python version, OS, dependencies)

2. Locate

• Read the full stack trace (bottom = where it crashed, top = root cause)
• Find the relevant file and line
• Read surrounding code for context

3. Understand

• What was the code trying to do?
• What input caused the failure?
• What assumption was violated?

4. Fix

• Make the minimal change that fixes the issue
• Don't refactor while debugging
• Add a test that would have caught this

5. Verify

• Run the failing case again
• Run the full test suite
• Check for similar patterns elsewhere

Common Patterns

NoneType errors: Something returned None unexpectedly. Check the call chain.

Import errors: Missing dependency or circular import. Check requirements and import order.

Key/Index errors: Accessing something that doesn't exist. Add existence checks.

Type errors: Wrong type passed. Check function signatures and callers.

Workflow

1. grep for the error message in codebase
2. Read the stack trace bottom-to-top
3. Read the failing function
4. Add logging/print if needed to trace values
5. Fix and verify