Guides code reviews of pull requests and diffs with principles for constructive feedback, architecture analysis, bug detection, and maintaining quality standards.
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Transform code reviews from gatekeeping to knowledge sharing through constructive feedback, systematic analysis, and collaborative improvement.
Goals of Code Review:
Not the Goals:
Good Feedback is:
❌ 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."
What to Review:
What Not to Review Manually:
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
Instead of stating problems, ask questions to encourage thinking:
❌ "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