gabrielmoreira Overview
Random code changes in response to errors are not debugging — they're noise generation. This skill enforces a systematic, hypothesis-driven approach: understand the problem, form a hypothesis, test it, confirm the root cause, then fix.
AI agents often cycle through random fixes until something "works." This skill prevents that.
When to Use
- Any time a test fails unexpectedly
- Any time you encounter an error or exception
- When behavior differs between environments
- When performance degrades unexpectedly
Process
Step 1: Reproduce Reliably
- Before doing anything else: reproduce the bug reliably. If you can't reproduce it, you can't fix it.
- Write a failing test that captures the bug — this becomes your regression test.
- Note the exact conditions that trigger the bug: inputs, environment, sequence of actions.
Verify: You can trigger the bug on demand.
Step 2: Understand Before Diagnosing
- Read the full error message — not just the first line.
- Read the stack trace from bottom to top — the root cause is usually near the bottom.
- Identify: What was the program trying to do? What happened instead?
Verify: You can explain the bug in one sentence without using the word "error."
Step 3: Form a Hypothesis
- Based on what you know, form a specific hypothesis: "I think the bug is X because Y."
- The hypothesis must be falsifiable — you can design a test that proves or disproves it.
- Do not start making code changes until you have a hypothesis.
Verify: Your hypothesis is specific enough to design a test for.
Step 4: Test the Hypothesis
- Add targeted logging or a targeted test that confirms or refutes the hypothesis.
- Run it. Read the output carefully.
- If the hypothesis is wrong: update your understanding, form a new hypothesis, repeat.
- If the hypothesis is right: you've found the root cause.
Verify: Root cause is confirmed by evidence, not assumed.
Step 5: Fix the Root Cause (Not the Symptom)
- Fix the root cause — not the symptom. Suppressing an error message is not a fix.
- Make the minimum change that fixes the root cause.
- Run the failing test you wrote in Step 1 — it should now pass.
- Run the full test suite — no regressions.
Verify: The specific failing test now passes. Full suite still passes.
Step 6: Prevent Recurrence
- If the bug wasn't caught by existing tests: add a test that would have caught it.
- If the bug was caused by a bad assumption: document the assumption or add a guard.
- Consider: does this class of bug exist elsewhere in the codebase?
Common Rationalizations (and Rebuttals)
| Excuse | Rebuttal |
|---|---|
| "Let me just try this and see" | Random changes produce random results. Form a hypothesis first. |
| "It must be a framework bug" | It's almost never the framework. Prove it before blaming it. |
| "Works on my machine" | Environment differences are root causes. Find them. Don't dismiss them. |
| "I'll add a try/catch" | That hides the bug. Find and fix the root cause. |
Red Flags
- Making code changes before understanding the bug
- Adding try/catch to silence errors without investigating root cause
- "I'll try this and see if it helps"
- Assuming the bug is in a dependency before proving it
- Fixing the symptom (error message) rather than the cause
Verification
- Bug reproducible on demand
- Root cause identified (not just symptom)
- Fix targets root cause, not symptom
- Reproduction test written and now passes
- Full test suite passes with no regressions
- Regression test added to prevent future occurrence