Debug

Systematic debugging for errors, test failures, and unexpected behavior.

When to Use

• Error messages or stack traces appear
• Tests are failing
• Code behaves unexpectedly
• User says "it's broken" or "not working"
• Need to find root cause of an issue

Debugging Process

1. Capture - Get error message, stack trace, and reproduction steps
2. Isolate - Narrow down the failure location
3. Hypothesize - Form theories about the cause
4. Test - Validate hypotheses with evidence
5. Fix - Implement minimal fix
6. Verify - Confirm solution works

Investigation Steps

# Check recent changes that might have caused the issue
git log --oneline -10
git diff HEAD~3

# Find error patterns in logs
grep -r "error\|Error\|ERROR" logs/ 2>/dev/null | tail -20

# Check test output
npm test 2>&1 | tail -50  # or pytest, cargo test, etc.

Output Format

## Debug Report

**Issue:** [Brief description]
**Root Cause:** [What's actually wrong]

### Evidence

- [Finding 1]
- [Finding 2]

### Fix

[Code or configuration change]

### Verification

[How to confirm the fix works]

### Prevention

[How to prevent this in the future]

Examples

Input: "TypeError: Cannot read property 'map' of undefined" Action: Trace the undefined value, find where data should be initialized, fix the source

Input: "Tests are failing" Action: Run tests, capture failures, analyze each failure, fix underlying issues