Code reviews are one of the most valuable practices a development team can adopt. Done well, they catch bugs, spread knowledge, and improve code quality. Done poorly, they become bottlenecks that frustrate everyone involved. Here's how to do them right.
Beyond Bug Catching
Most people think code reviews are about finding bugs. They are, but that's not their primary value. Automated tests catch most bugs more reliably than human reviewers.
The real benefits of code review are:
Knowledge sharing: Reviews expose everyone to code they didn't write. When someone goes on vacation or leaves the company, others can maintain their code.
Mentorship: Junior developers learn by having their code reviewed. Senior developers reinforce their knowledge by explaining their feedback.
Consistency: Reviews enforce team standards. Code starts looking like it came from one team rather than many individuals.
Early design feedback: It's cheaper to change code during review than after it's been deployed and other code depends on it.
What to Look For
Logic and Correctness
Does the code do what it's supposed to do? Read the requirements or ticket, then verify the implementation matches.
Look for edge cases:
- What happens with empty inputs?
- What about null values?
- Are there potential division-by-zero errors?
- What happens at boundaries (first item, last item, zero, maximum value)?
Code Readability
Code is read far more often than it's written. Prioritize clarity over cleverness.
Ask yourself:
- Can you understand what this code does without the author explaining it?
- Are variable names descriptive?
- Are functions focused on one task?
- Are there comments where logic is non-obvious?
// Hard to read
$x = array_filter($a, fn($i) => $i->s === 'a' && $i->d < now());
// Easier to read
$activeItems = array_filter($items, function ($item) {
return $item->status === 'active'
&& $item->deadline->isPast();
});
Performance Implications
Not every review needs deep performance analysis, but watch for obvious issues:
- N+1 queries (especially in loops)
- Loading large datasets into memory unnecessarily
- Synchronous operations that should be queued
- Missing database indexes for new queries
Security Concerns
Security vulnerabilities are expensive to fix after deployment. Look for:
- Raw SQL queries with user input
- Missing input validation
- Sensitive data in logs
- Authorization checks (can this user perform this action?)
- CSRF tokens in forms
- Output escaping in views
Test Coverage
Does the code have tests? Do the tests actually verify the behavior, or do they just exercise the code without meaningful assertions?
Watch for:
- Tests that can never fail
- Missing edge case tests
- Tests that depend on external services
- Tests that test implementation details rather than behavior
Giving Constructive Feedback
Be Kind and Professional
Remember there's a person on the other end of your comments. Critique the code, not the coder.
Instead of:
This is wrong. You should never do it this way.
Write:
This approach might cause N+1 queries. Consider using eager loading instead.
Explain Why
Don't just say what to change;explain why. This helps the author learn and makes them more likely to accept the feedback.
Instead of:
Change this to use a constant.
Write:
Magic numbers make code harder to maintain. Let's extract this to a constant with a descriptive name so future readers understand what 86400 represents.
Distinguish Preferences from Problems
Not every comment is equally important. Use a convention to indicate severity:
- Blocking: Must be fixed before merge
- Non-blocking: Suggestion for improvement, but not required
- Nitpick: Personal preference, take it or leave it
Some teams use prefixes like [blocking] or [nit] to make this clear.
Ask Questions
When you're unsure, ask rather than assert. Questions are less confrontational and might reveal context you're missing.
Why did you choose to implement it this way? I'm wondering if X approach might be simpler.
Praise Good Work
Code review shouldn't be exclusively negative. When you see something done well, say so:
Nice use of the null object pattern here. Much cleaner than the null checks we had before.
Receiving Feedback Gracefully
Don't Take It Personally
Feedback on your code is not feedback on your worth as a developer. Everyone's code can be improved.
Assume Good Intent
If a comment seems harsh, assume the reviewer didn't intend it that way. Text lacks tone. When in doubt, ask for clarification in person.
Learn from Every Review
Each piece of feedback is an opportunity to learn something. Even if you disagree, try to understand the reviewer's perspective.
Know When to Push Back
Not every suggestion is correct. If you disagree, explain your reasoning. A good discussion often leads to a better solution than either person proposed initially.
I considered that approach, but it would require loading all related records upfront. In this case, we only need them conditionally, so lazy loading seems appropriate.
Efficient Review Workflows
Keep Pull Requests Small
Large pull requests get superficial reviews. Reviewers' attention is finite. A 50-line PR gets careful review; a 500-line PR gets skimmed.
Aim for PRs that:
- Focus on one logical change
- Can be reviewed in 15-30 minutes
- Have clear descriptions of what changed and why
Review Promptly
Stale PRs slow everyone down. The author has moved on mentally and must context-switch back when reviews come in. Other work may pile up behind the blocked change.
Set expectations as a team. Many teams aim to provide initial review within one business day.
Use Your Tools
Modern code review platforms offer features that help:
- Suggested changes: Propose specific edits that authors can accept with one click
- Code owners: Automatically request review from relevant people
- Required reviews: Prevent merging until designated reviewers approve
- Status checks: Block merging until tests pass
Don't Review What Machines Can Check
Automated tools should catch formatting issues, linting errors, and type mismatches. Don't spend human attention on what CI can verify.
Run these checks before requesting review, so reviewers focus on design and logic rather than syntax.
Building a Review Culture
Lead by Example
Senior developers should have their code reviewed too. This normalizes the practice and shows that review is about code quality, not developer seniority.
Rotate Reviewers
Don't let the same person review all code. Rotation spreads knowledge and prevents bottlenecks when key people are unavailable.
Discuss Standards as a Team
When disagreements arise repeatedly, discuss them as a team and document decisions. This prevents the same discussions from recurring in every review.
Measure and Improve
Track metrics like:
- Time from PR opened to first review
- Time from PR opened to merge
- Number of review cycles before merge
Use these to identify bottlenecks and improve your process.
Conclusion
Code review is a skill that improves with practice. Both giving and receiving feedback get easier over time. The investment pays off in higher quality code, shared knowledge, and a collaborative team culture.
Start with small changes if your team doesn't review code today. Even informal reviews help. As the practice matures, add structure and tooling to make reviews more efficient.
The best code review processes feel natural;they're part of how the team works, not an obstacle to shipping. That takes time and intentional effort to build, but the results are worth it.