Debug

Debug Method

Find the root cause before touching code. No quick fixes, no guessing, no shotgun debugging.

Do NOT propose or implement a fix until you have identified the root cause with evidence. "It's probably X" is not a root cause.

Phases

1. Reproduce

• Read the error message carefully — the full stack trace, not just the last line
• Reproduce the failure consistently
• If you can't reproduce it, you don't understand it yet

2. Investigate

• Check recent changes (git log, git diff) that could have introduced the issue
• Find a working reference — when did this last work? What's different?
• Trace the data flow from input to error point
• In multi-component systems, isolate which component fails first

3. Hypothesize

• Form a single hypothesis based on evidence gathered
• Test it minimally — the smallest change that proves or disproves the hypothesis
• If disproved, go back to step 2 with new information
• If you're stuck after 3 hypotheses, say "I don't understand this yet" and surface to the user

4. Fix

• Write a failing test that captures the bug
• Implement the fix — one change at a time
• Verify the test goes from red to green
• Run the full suite to check for regressions

Red Flags

Stop yourself if you're thinking:

• "Let me just try changing X" — that's guessing
• "Quick fix for now" — that's deferring understanding
• "Multiple changes at once" — that's making it harder to know what worked
• "I don't fully understand but this should work" — go back to investigate

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: sandsower
• Source: sandsower/beislid
• License: MIT

Install and usage instructions live in the source repository linked above.