debug

Debug

Systematic root-cause analysis — reproduce, isolate, hypothesize, fix, verify.

Process

1. Read the error — full message, stack trace, error code. Don't skip this.
2. Reproduce reliably — minimal steps before touching any code.
3. Isolate — binary search via git bisect, comment blocks, or minimal repro.
4. Hypothesize — one specific theory. Don't change multiple things at once.
5. Test hypothesis — add logging, use debugger, modify code.
6. Apply minimal fix — smallest change that addresses root cause, not symptoms.
7. Verify — confirm fix works and no regressions.

Diagnosis Checklist

Start here before touching code:

• Read the full error message — it often tells you exactly what's wrong
• Check recent changes: git log --oneline -10 / git diff HEAD~1
• Check logs around time of failure
• Verify environment matches expected (versions, env vars, config)
• Could this be a race condition or timing issue?
• Is this intermittent or consistent?

Reproduction:

# Find the commit that introduced it
git bisect start
git bisect bad HEAD
git bisect good <last-known-good-sha>

Strategic logging:

// Entry/exit with parameters — temporary, remove after fix
console.log('[debug] functionName called', { param1, param2 });
// ...
console.log('[debug] functionName result', { result });

Anti-Patterns

• Don't make random changes hoping something fixes it — form a hypothesis first
• Don't fix symptoms without understanding root cause
• Don't debug in production without safeguards
• Don't leave debug logs or breakpoints in committed code
• Don't trust your mental model — read the actual code

Output

## Root Cause
[What actually caused the issue]

## Evidence
- [Log excerpt / stack trace / variable state]

## Fix
`file:line`
```diff
- broken code
+ fixed code

Why this fixes it: [reasoning]

Prevention

• [Recommendation to avoid recurrence]