Code Review Best Practices: A Senior Engineer's Guide

Code reviews are one of the most important practices in software development. They're not just about finding bugs—they're about sharing knowledge, maintaining code quality, and building better software together. After reviewing thousands of pull requests, I've learned what makes reviews effective and what doesn't.

The Purpose of Code Reviews

Code reviews serve multiple purposes:

1. Catch bugs - Find issues before they reach production
2. Share knowledge - Learn from each other
3. Maintain standards - Ensure consistency
4. Improve design - Discuss architecture decisions
5. Build team culture - Foster collaboration

What to Review

Functionality

Does the code do what it's supposed to do?

• Test the changes - Actually run the code
• Check edge cases - What happens with null, empty, or invalid input?
• Verify requirements - Does it meet the acceptance criteria?

Code Quality

Is the code maintainable?

• Readability - Can others understand it?
• Simplicity - Is it as simple as it can be?
• DRY - Don't Repeat Yourself
• SOLID principles - Is it well-designed?

Performance

Are there obvious performance issues?

• N+1 queries - Database queries in loops
• Unnecessary computations - Can it be cached or optimized?
• Memory leaks - Proper cleanup?

Security

Are there security vulnerabilities?

• Input validation - Sanitize user input
• Authentication/Authorization - Proper checks?
• Sensitive data - No secrets in code
• SQL injection - Use parameterized queries

Testing

Is the code tested?

• Unit tests - Logic is tested
• Integration tests - Components work together
• Test coverage - Critical paths are covered

How to Give Feedback

Be Constructive

Bad:

"This is wrong. Fix it."

Good:

"I think there might be an edge case here. What happens if user is null? Maybe we should add a null check or use optional chaining?"

Be Specific

Bad:

"This function is too complex."

Good:

"This function has 15 parameters and handles 5 different cases. Consider splitting it into smaller functions, each handling one case."

Explain Why

Bad:

"Use a map instead."

Good:

"Using a Map here would give us O(1) lookups instead of O(n) with an array. Since we're doing many lookups, this would improve performance."

Ask Questions

Bad:

"This won't work."

Good:

"I'm not sure I understand this approach. Could you explain why you chose this pattern? I'm wondering if there's a simpler way."

Praise Good Work

Good:

"Great use of the strategy pattern here! This makes it easy to add new payment methods."

"I really like how you've extracted this into a reusable hook. This will be useful in other components."

Review Checklist

Use this checklist for consistent reviews:

• Code follows project style guide
• No obvious bugs or logic errors
• Edge cases are handled
• Error handling is appropriate
• Code is readable and well-commented
• No security vulnerabilities
• Performance considerations addressed
• Tests are included and pass
• Documentation updated if needed
• No commented-out code
• No debugging code left in

Common Issues to Look For

1. Magic Numbers

// Bad
if (status === 3) {
  // What is 3?
}

// Good
const ORDER_STATUS = {
  PENDING: 1,
  PROCESSING: 2,
  COMPLETED: 3
};

if (status === ORDER_STATUS.COMPLETED) {
  // Clear intent
}

2. Long Functions

Functions should do one thing. If a function is longer than 20-30 lines, consider splitting it.

3. Deep Nesting

// Bad
if (user) {
  if (user.isActive) {
    if (user.hasPermission) {
      // Do something
    }
  }
}

// Good
if (!user || !user.isActive || !user.hasPermission) {
  return;
}
// Do something

4. Inconsistent Error Handling

// Bad: Inconsistent
try {
  const user = await getUser(id);
} catch (error) {
  console.log(error); // Sometimes
  throw error; // Sometimes
  return null; // Sometimes
}

// Good: Consistent
try {
  const user = await getUser(id);
  return { success: true, data: user };
} catch (error) {
  logger.error('Failed to get user', { id, error });
  return { success: false, error: error.message };
}

5. Missing Tests

Always ask: "How do we know this works?"

Reviewing Large PRs

Large PRs are hard to review. Here's how to handle them:

1. Ask for Smaller PRs

"This PR has 50 files changed. Could we split this into smaller PRs? Maybe one for the API changes and one for the UI changes?"

2. Review in Phases

• First pass: Overall architecture and design
• Second pass: Implementation details
• Third pass: Edge cases and testing

3. Focus on Critical Paths

Review the most important parts first:

• Core business logic
• Security-sensitive code
• Performance-critical paths

Handling Disagreements

Stay Professional

Remember: You're reviewing code, not the person.

Discuss, Don't Dictate

"I see you chose approach A. I was thinking approach B might work better because [reason]. What do you think?"

Defer to the Author

If it's a matter of style and both approaches work, let the author decide.

Escalate When Needed

If there's a fundamental disagreement about architecture, involve the team lead or architect.

Time Management

Review Promptly

Aim to review within 24 hours. Blocked PRs slow down the team.

Set Aside Time

Schedule time for code reviews. Don't try to squeeze them in between other tasks.

Use Tools

• GitHub's "Suggest Changes" feature
• Automated tools for style issues
• Linters and formatters

Learning from Reviews

As a Reviewer

• Learn new patterns and approaches
• See how others solve problems
• Stay aware of codebase changes

As an Author

• Ask questions about feedback
• Understand the "why" behind suggestions
• Apply learnings to future code

Real-World Example

Scenario: PR adds a new feature with 20 files changed.

Review Approach:

1. First pass (10 min): Read PR description, check overall structure
2. Second pass (30 min): Review core logic, check for bugs
3. Third pass (20 min): Check tests, edge cases, documentation

Feedback Given:

• ✅ "Great job on the error handling!"
• ❓ "I'm not sure about this approach. Could we discuss?"
• 🔧 "This could be simplified. Here's a suggestion..."
• 🐛 "I think there's a bug here when user is null."

Result: PR improved, author learned, team knowledge shared.

Best Practices Summary

1. Review promptly - Don't block others
2. Be constructive - Help, don't criticize
3. Explain why - Context matters
4. Ask questions - Learn together
5. Praise good work - Positive reinforcement
6. Focus on what matters - Don't nitpick style
7. Keep PRs small - Easier to review
8. Automate what you can - Linters, formatters
9. Learn continuously - Every review is a learning opportunity

Conclusion

Effective code reviews are a skill that improves with practice. The goal isn't to find every possible issue—it's to:

• Improve code quality
• Share knowledge
• Build better software
• Strengthen the team

Remember: The best code reviews are conversations, not critiques. Approach them with curiosity and a desire to help, and you'll see the quality of your codebase—and your team—improve.

What code review practices have worked best for your team? I'd love to hear about your experiences.