TSS-Blue-AI-Lab Bug Fixer
Find and fix bugs systematically instead of guessing.
When to Use
- An error or exception is thrown
- A feature doesn't work as expected
- Tests are failing
- Users report unexpected behavior
- Something worked before but broke after a change
How It Works
1. Reproduce First
Never fix what you can't reproduce:
1. Get the exact error message or unexpected behavior
2. Find the minimal steps to trigger it
3. Confirm you can see the bug consistently
2. Read the Error
Most bugs tell you exactly what's wrong:
Error: Cannot read properties of undefined (reading 'map')
at UserList (src/components/UserList.tsx:12:24)
at Dashboard (src/app/dashboard/page.tsx:8:5)
Parse it:
- What: trying to call
.map()onundefined - Where:
UserList.tsx, line 12 - Why: the data hasn't loaded yet (undefined instead of array)
3. Narrow the Scope
Work from the error outward:
1. Go to the exact file and line from the error
2. Trace the data flow backward:
- Where does this variable come from?
- What function returns it?
- What API provides it?
3. Find where expected value diverges from actual value
4. Common Bug Patterns
| Symptom | Likely Cause | Fix |
|---|---|---|
undefined is not a function |
Wrong import or typo | Check import path and export name |
Cannot read property of undefined |
Missing null check or data not loaded | Add optional chaining (?.) or loading state |
Too many re-renders |
State update in render body | Move to useEffect or event handler |
Hydration mismatch |
Server/client HTML differs | Use useEffect for client-only content |
| API returns 500 | Unhandled error in backend | Check server logs, add try/catch |
| Stale data in UI | Missing cache invalidation | Revalidate after mutation |
| Works locally, fails in CI | Environment difference | Check env vars, Node version, dependencies |
5. Fix and Verify
1. Make the smallest possible change that fixes the bug
2. Run the failing test / reproduce steps — confirm it passes
3. Check for similar patterns elsewhere in the code
4. Add a test that would catch this bug in the future
6. Debugging Commands
# Check recent changes that may have caused the bug
git log --oneline -10
git diff HEAD~3
# Find where a variable is used
grep -rn "variableName" src/
# Check TypeScript errors
npx tsc --noEmit
# Run a specific test
npx jest path/to/test --verbose
Quality Checklist
- Bug is reproducible before fixing
- Fix is minimal (no unrelated changes)
- Existing tests still pass
- New test added to prevent regression
- No console.log left in code
Examples
> Fix this error: TypeError: Cannot read properties of null (reading 'id')
> The login form submits but nothing happens — debug it
> Tests pass locally but fail in CI — investigate