❌ Bad: "This is wrong." ✅ Good: "This could cause a race condition when multiple users access simultaneously. Consider using a mutex here."

❌ Bad: "Why didn't you use X pattern?" ✅ Good: "Have you considered the Repository pattern? It would make this easier to test. Here's an example: [link]"

❌ Bad: "Rename this variable." ✅ Good: "[nit] Consider `userCount` instead of `uc` for clarity. Not blocking if you prefer to keep it."

Before diving into code, understand:

1. Read PR description and linked issue
2. Check PR size (>400 lines? Ask to split)
3. Review CI/CD status (tests passing?)
4. Understand the business requirement
5. Note any relevant architectural decisions

1. **Architecture & Design**

   - Does the solution fit the problem?
   - Are there simpler approaches?
   - Is it consistent with existing patterns?
   - Will it scale?

2. **File Organization**

   - Are new files in the right places?
   - Is code grouped logically?
   - Are there duplicate files?

3. **Testing Strategy**
   - Are there tests?
   - Do tests cover edge cases?
   - Are tests readable?

For each file:

1. **Logic & Correctness**

   - Edge cases handled?
   - Off-by-one errors?
   - Null/undefined checks?
   - Race conditions?

2. **Security**

   - Input validation?
   - SQL injection risks?
   - XSS vulnerabilities?
   - Sensitive data exposure?

3. **Performance**

   - N+1 queries?
   - Unnecessary loops?
   - Memory leaks?
   - Blocking operations?

4. **Maintainability**
   - Clear variable names?
   - Functions doing one thing?
   - Complex code commented?
   - Magic numbers extracted?

1. Summarize key concerns
2. Highlight what you liked
3. Make clear decision:
   - ✅ Approve
   - 💬 Comment (minor suggestions)
   - 🔄 Request Changes (must address)
4. Offer to pair if complex

## Security Checklist

- [ ] User input validated and sanitized
- [ ] SQL queries use parameterization
- [ ] Authentication/authorization checked
- [ ] Secrets not hardcoded
- [ ] Error messages don't leak info

## Performance Checklist

- [ ] No N+1 queries
- [ ] Database queries indexed
- [ ] Large lists paginated
- [ ] Expensive operations cached
- [ ] No blocking I/O in hot paths

## Testing Checklist

- [ ] Happy path tested
- [ ] Edge cases covered
- [ ] Error cases tested
- [ ] Test names are descriptive
- [ ] Tests are deterministic

❌ "This will fail if the list is empty." ✅ "What happens if `items` is an empty array?"

❌ "You need error handling here." ✅ "How should this behave if the API call fails?"

❌ "This is inefficient." ✅ "I see this loops through all users. Have we considered the performance impact with 100k users?"

## Use Collaborative Language

❌ "You must change this to use async/await" ✅ "Suggestion: async/await might make this more readable: `typescript     async function fetchUser(id: string) {         const user = await db.query('SELECT * FROM users WHERE id = ?', id);         return user;     }     ` What do you think?"

❌ "Extract this into a function" ✅ "This logic appears in 3 places. Would it make sense to extract it into a shared utility function?"

Use labels to indicate priority:

🔴 [blocking] - Must fix before merge 🟡 [important] - Should fix, discuss if disagree 🟢 [nit] - Nice to have, not blocking 💡 [suggestion] - Alternative approach to consider 📚 [learning] - Educational comment, no action needed 🎉 [praise] - Good work, keep it up!

Example: "🔴 [blocking] This SQL query is vulnerable to injection. Please use parameterized queries."

"🟢 [nit] Consider renaming `data` to `userData` for clarity."

"🎉 [praise] Excellent test coverage! This will catch edge cases."

# Check for Python-specific issues

# ❌ Mutable default arguments
def add_item(item, items=[]):  # Bug! Shared across calls
    items.append(item)
    return items

# ✅ Use None as default
def add_item(item, items=None):
    if items is None:
        items = []
    items.append(item)
    return items

# ❌ Catching too broad
try:
    result = risky_operation()
except:  # Catches everything, even KeyboardInterrupt!
    pass

# ✅ Catch specific exceptions
try:
    result = risky_operation()
except ValueError as e:
    logger.error(f"Invalid value: {e}")
    raise

# ❌ Using mutable class attributes
class User:
    permissions = []  # Shared across all instances!

# ✅ Initialize in __init__
class User:
    def __init__(self):
        self.permissions = []

// Check for TypeScript-specific issues

// ❌ Using any defeats type safety
function processData(data: any) {  // Avoid any
    return data.value;
}

// ✅ Use proper types
interface DataPayload {
    value: string;
}
function processData(data: DataPayload) {
    return data.value;
}

// ❌ Not handling async errors
async function fetchUser(id: string) {
    const response = await fetch(`/api/users/${id}`);
    return response.json();  // What if network fails?
}

// ✅ Handle errors properly
async function fetchUser(id: string): Promise<User> {
    try {
        const response = await fetch(`/api/users/${id}`);
        if (!response.ok) {
            throw new Error(`HTTP ${response.status}`);
        }
        return await response.json();
    } catch (error) {
        console.error('Failed to fetch user:', error);
        throw error;
    }
}

// ❌ Mutation of props
function UserProfile({ user }: Props) {
    user.lastViewed = new Date();  // Mutating prop!
    return <div>{user.name}</div>;
}

// ✅ Don't mutate props
function UserProfile({ user, onView }: Props) {
    useEffect(() => {
        onView(user.id);  // Notify parent to update
    }, [user.id]);
    return <div>{user.name}</div>;
}

When reviewing significant changes:

1. **Design Document First**

   - For large features, request design doc before code
   - Review design with team before implementation
   - Agree on approach to avoid rework

2. **Review in Stages**

   - First PR: Core abstractions and interfaces
   - Second PR: Implementation
   - Third PR: Integration and tests
   - Easier to review, faster to iterate

3. **Consider Alternatives**
   - "Have we considered using [pattern/library]?"
   - "What's the tradeoff vs. the simpler approach?"
   - "How will this evolve as requirements change?"

// ❌ Poor test: Implementation detail testing
test('increments counter variable', () => {
    const component = render(<Counter />);
    const button = component.getByRole('button');
    fireEvent.click(button);
    expect(component.state.counter).toBe(1);  // Testing internal state
});

// ✅ Good test: Behavior testing
test('displays incremented count when clicked', () => {
    render(<Counter />);
    const button = screen.getByRole('button', { name: /increment/i });
    fireEvent.click(button);
    expect(screen.getByText('Count: 1')).toBeInTheDocument();
});

// Review questions for tests:
// - Do tests describe behavior, not implementation?
// - Are test names clear and descriptive?
// - Do tests cover edge cases?
// - Are tests independent (no shared state)?
// - Can tests run in any order?

## Security Review Checklist

### Authentication & Authorization

- [ ] Is authentication required where needed?
- [ ] Are authorization checks before every action?
- [ ] Is JWT validation proper (signature, expiry)?
- [ ] Are API keys/secrets properly secured?

### Input Validation

- [ ] All user inputs validated?
- [ ] File uploads restricted (size, type)?
- [ ] SQL queries parameterized?
- [ ] XSS protection (escape output)?

### Data Protection

- [ ] Passwords hashed (bcrypt/argon2)?
- [ ] Sensitive data encrypted at rest?
- [ ] HTTPS enforced for sensitive data?
- [ ] PII handled according to regulations?

### Common Vulnerabilities

- [ ] No eval() or similar dynamic execution?
- [ ] No hardcoded secrets?
- [ ] CSRF protection for state-changing operations?
- [ ] Rate limiting on public endpoints?

Traditional: Praise + Criticism + Praise (feels fake)

Better: Context + Specific Issue + Helpful Solution

Example: "I noticed the payment processing logic is inline in the controller. This makes it harder to test and reuse.

[Specific Issue] The calculateTotal() function mixes tax calculation, discount logic, and database queries, making it difficult to unit test and reason about.

[Helpful Solution] Could we extract this into a PaymentService class? That would make it testable and reusable. I can pair with you on this if helpful."

When author disagrees with your feedback:

1. **Seek to Understand** "Help me understand your approach. What led you to choose this pattern?"

2. **Acknowledge Valid Points** "That's a good point about X. I hadn't considered that."

3. **Provide Data** "I'm concerned about performance. Can we add a benchmark to validate the approach?"

4. **Escalate if Needed** "Let's get [architect/senior dev] to weigh in on this."

5. **Know When to Let Go** If it's working and not a critical issue, approve it. Perfection is the enemy of progress.

## Summary

[Brief overview of what was reviewed]

## Strengths

- [What was done well]
- [Good patterns or approaches]

## Required Changes

🔴 [Blocking issue 1] 🔴 [Blocking issue 2]

## Suggestions

💡 [Improvement 1] 💡 [Improvement 2]

## Questions

❓ [Clarification needed on X] ❓ [Alternative approach consideration]

## Verdict

✅ Approve after addressing required changes