bug-hunter

2

sickn33/agentic-awesome-skillsAudit passedSnapshot 7c5a5a121705

Summary

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SKILL.md

Bug Hunter

Systematically hunt down and fix bugs using proven debugging techniques. No guessing—follow the evidence.

When to Use This Skill

User reports a bug or error
Something isn't working as expected
User says "fix the bug" or "debug this"
Intermittent failures or weird behavior
Production issues need investigation

The Debugging Process

1. Reproduce the Bug

First, make it happen consistently:

1. Get exact steps to reproduce
2. Try to reproduce locally
3. Note what triggers it
4. Document the error message/behavior
5. Check if it happens every time or randomly

If you can't reproduce it, gather more info:

What environment? (dev, staging, prod)
What browser/device?
What user actions preceded it?
Any error logs?

2. Gather Evidence

Collect all available information:

Check logs:

# Application logs
tail -f logs/app.log

# System logs
journalctl -u myapp -f

# Browser console
# Open DevTools → Console tab

Check error messages:

Full stack trace
Error type and message
Line numbers
Timestamp

Check state:

What data was being processed?
What was the user trying to do?
What's in the database?
What's in local storage/cookies?

3. Form a Hypothesis

Based on evidence, guess what's wrong:

"The login times out because the session cookie 
expires before the auth check completes"

"The form fails because email validation regex 
doesn't handle plus signs"

"The API returns 500 because the database query 
has a syntax error with special characters"

4. Test the Hypothesis

Prove or disprove your guess:

Add logging:

console.log('Before API call:', userData);
const response = await api.login(userData);
console.log('After API call:', response);

debugger; // Execution pauses here
const result = processData(input);

// Comment out code to narrow down
// const result = complexFunction();
const result = { mock: 'data' }; // Use mock data

Symptom: "Cannot read property 'name' of undefined"
↓
Where: user.profile.name
↓
Why: user.profile is undefined
↓
Why: API didn't return profile
↓
Why: User ID was null
↓
Root cause: Login didn't set user ID in session

// Just hide the error
const name = user?.profile?.name || 'Unknown';

// Ensure user ID is set on login
const login = async (credentials) => {
  const user = await authenticate(credentials);
  if (user) {
    session.userId = user.id; // Fix: Set user ID
    return user;
  }
  throw new Error('Invalid credentials');
};

1. Reproduce the original bug
2. Apply the fix
3. Try to reproduce again (should fail)
4. Test edge cases
5. Test related functionality
6. Run existing tests

test('login sets user ID in session', async () => {
  const user = await login({ email: '[email protected]', password: 'pass' });
  
  expect(session.userId).toBe(user.id);
  expect(session.userId).not.toBeNull();
});

// Does the bug happen before or after this line?
console.log('CHECKPOINT 1');
// ... code ...
console.log('CHECKPOINT 2');
// ... code ...
console.log('CHECKPOINT 3');

console.log('Input:', input);
console.log('After transform:', transformed);
console.log('Before save:', data);
console.log('Result:', result);

git bisect start
git bisect bad  # Current commit is broken
git bisect good abc123  # This old commit worked
# Git will check out commits for you to test

// Bug
const name = user.profile.name;

// Fix
const name = user?.profile?.name || 'Unknown';

// Better fix
if (!user || !user.profile) {
  throw new Error('User profile required');
}
const name = user.profile.name;

// Bug
let data = null;
fetchData().then(result => data = result);
console.log(data); // null - not loaded yet

// Fix
const data = await fetchData();
console.log(data); // correct value

// Bug
for (let i = 0; i <= array.length; i++) {
  console.log(array[i]); // undefined on last iteration
}

// Fix
for (let i = 0; i < array.length; i++) {
  console.log(array[i]);
}

// Bug
if (count == 0) { // true for "", [], null
  
// Fix
if (count === 0) { // only true for 0

// Bug
const result = asyncFunction(); // Returns Promise
console.log(result.data); // undefined

// Fix
const result = await asyncFunction();
console.log(result.data); // correct value

Console: View logs and errors
Sources: Set breakpoints, step through code
Network: Check API calls and responses
Application: View cookies, storage, cache
Performance: Find slow operations

// Built-in debugger
node --inspect app.js

// Then open chrome://inspect in Chrome

// .vscode/launch.json
{
  "type": "node",
  "request": "launch",
  "name": "Debug App",
  "program": "${workspaceFolder}/app.js"
}

## Bug: Login timeout after 30 seconds

**Symptom:** Users get logged out immediately after login

**Root Cause:** Session cookie expires before auth check completes

**Fix:** Increased session timeout from 30s to 3600s in config

**Files Changed:**
- config/session.js (line 12)

**Testing:** Verified login persists for 1 hour

**Prevention:** Added test for session persistence