Code Review Best Practices

Updated March 2026 12 min read Intermediate

Code reviews are one of the most valuable practices in software development. They catch bugs, spread knowledge, and improve code quality. This guide will help you master the art of giving and receiving feedback effectively.

Approve Comment Request Changes

Why Code Reviews Matter

Code reviews are far more than just a quality gate. They serve multiple critical functions in a healthy development team. First, they catch bugs and edge cases that the original author might have missed. Studies show that code reviews can identify 60-90% of defects before they ever reach production.

Beyond bug prevention, code reviews are an essential knowledge-sharing mechanism. When a developer submits a pull request, the review process ensures that at least one other person understands the code. This creates bus factor protection and spreads expertise across the team. New team members learn the codebase faster by reviewing and being reviewed. Finally, consistent reviews help maintain coding standards and architectural consistency across the entire codebase.

Research indicates that teams with healthy code review cultures ship 50% faster and have significantly lower defect rates than teams that skip reviews.

How to Review a Pull Request

An effective code review follows a structured approach. Start by understanding the context: read the pull request description carefully and review any linked issues or requirements. Before diving into code, consider whether the overall approach solves the problem correctly. Does it align with the project's architecture? Could there be a simpler way?

Next, examine the code incrementally. Focus on the most important files first. Look for clarity and readability—code is read far more often than it is written. Check that there are appropriate tests covering both happy paths and edge cases. When you find issues, leave specific, actionable feedback. Instead of saying "this is wrong," explain what you'd suggest and why. End by submitting your review with one of the three statuses: approve, comment, or request changes.

When possible, run the code locally. Nothing catches subtle issues like seeing the change in action.

Writing Constructive Comments

The language you use in code review comments has a huge impact on how they're received. Good feedback focuses on the code, not the person. Rather than saying "you did this wrong," try phrasing it as "this part could be improved by..." or "what do you think about trying X approach?" Asking questions is often more effective than making demands. A question like "could this handle the case where the list is empty?" invites collaboration rather than defensiveness.

When you have a suggestion, be specific about what you'd change and why. Explain the reasoning behind your feedback—"this would be more maintainable because..." or "this pattern helps with performance because...". This helps the author learn rather than just accept changes. For minor style preferences or non-blocking suggestions, mark them clearly as "nit:" or "optional:" so the author knows they can decide.

Instead of: "This is inefficient."
Try: "We could optimize this by moving the API call outside the loop. Since the data doesn't change between iterations, making one request would be more efficient."

Remember: you're reviewing code, not judging the developer. Assume positive intent and focus on making the code better together.

GitHub Suggestions: Propose Exact Changes

One of GitHub's most powerful code review features is the ability to suggest specific code changes. When you're reviewing a pull request, you can click the plus icon next to any line of code and type your suggested alternative. GitHub formats it as a suggestion block with an "Add suggestion" button. The author can then apply your suggestion with a single click, saving time and reducing back-and-forth.

Suggestions are particularly useful for catching typos, naming improvements, small refactors, or adding missing error handling. Instead of describing what you want, you can show exactly what you mean. This clarity reduces misunderstandings and makes the review process more efficient for everyone.

                ```suggestion

const user = await User.findById(userId);

if (!user) {

  throw new Error('User not found');

}

```

The author can then click "Commit suggestion" to add your changes directly to the branch, with you credited as the co-author.

How to Respond to Code Review Feedback

Being reviewed is a skill just as important as reviewing. When you receive feedback, start by thanking the reviewer for their time and attention. Remember that feedback is about the code, not about you as a developer. Even experienced engineers learn new things from reviews—embrace that growth opportunity.

When you agree with feedback, apply the changes promptly. For suggestions, use GitHub's "Commit suggestion" feature. For feedback that requires more discussion, respond respectfully with your reasoning. If you disagree, explain your perspective with evidence or examples. Sometimes a quick discussion leads to an even better solution than either original approach. When you make changes, leave a comment to let the reviewer know they're ready for another look.

Example response: "Thanks for the thoughtful review! I've applied your suggestion for the error handling. The reason I used a loop initially was to handle multiple items, but I agree the map approach is cleaner. Ready for another look when you have time."

PR Size and Review Timing

The size of a pull request dramatically affects review quality. Research shows that as pull requests grow beyond 400 lines, the number of bugs found per line drops significantly. Reviewers get fatigued and start skimming rather than carefully examining code. For this reason, it's best to keep pull requests focused on a single logical change. If you're making multiple unrelated changes, split them into separate PRs.

Review timing also matters. The best practice is to review pull requests within 24 hours. Long wait times frustrate authors and slow down the entire team. When you're reviewing, limit review sessions to 60 minutes maximum. After that, your attention starts to fade, and you're more likely to miss issues. If a PR is large, review it in multiple sessions or ask the author to split it.

Small, focused PRs are reviewed faster and more thoroughly. They also make it easier to revert changes if something goes wrong.

Building a Positive Review Culture

A healthy code review culture doesn't happen by accident—it's built through consistent practice and intentional behavior. Start by recognizing that code reviews are a team activity. Everyone is working toward the same goal: making the codebase better. When you review, look for things to praise as well as things to improve. Acknowledging good decisions and clever solutions makes the process feel more balanced and collaborative.

Encourage knowledge sharing by rotating reviewers. When different team members review different PRs, expertise spreads naturally across the team. Use automation to handle routine checks like formatting and basic linting—let humans focus on logic, design, and edge cases. Finally, celebrate good reviews. When someone provides especially helpful feedback, acknowledge it in team meetings or retrospectives. This reinforces the behavior you want to see.

Teams with positive, collaborative review cultures report higher job satisfaction, lower turnover, and faster delivery times.

Frequently Asked Questions

How many reviewers should I request?

For most teams, one to two reviewers is ideal. More than that creates coordination overhead and slows down shipping. For critical security changes or major architectural work, two reviewers is a common practice. One reviewer is usually sufficient for routine changes.

What's the difference between "Request changes" and "Comment"?

Request changes blocks merging until the requested changes are made. Use this when there are issues that must be fixed for the code to be acceptable. Comment is for suggestions, questions, or optional feedback—the PR can still be merged without addressing them. When in doubt, use comment with a clear "optional" label.

How do I handle style disagreements?

For coding style, defer to your project's style guide and automated formatters like Prettier or Black. If there's no established style, the author's preference often wins for subjective choices. For major architectural disagreements, involve the whole team in a discussion rather than fighting in a PR comment thread.

What if the author and reviewer disagree on approach?

First, try to understand each other's perspective through respectful discussion. Sometimes a video call or quick chat resolves misunderstandings faster than written comments. If you're still stuck, bring in a third team member as a tiebreaker. For significant decisions, document the reasoning so future reviewers understand the context.

How do I review a PR when I'm not familiar with that part of the codebase?

That's a learning opportunity! Focus on what you can evaluate: readability, naming clarity, test coverage, and whether the approach seems reasonable. Ask clarifying questions—they help both you learn and the author explain their reasoning. Your fresh perspective can catch assumptions that more familiar reviewers might miss.

What security issues should I look for in code reviews?

Pay attention to: hardcoded secrets or API keys, SQL injection vulnerabilities (especially string concatenation in queries), XSS risks in user-generated content, insecure authentication patterns, and outdated or vulnerable dependencies. Tools like CodeQL can automate much of this, but human reviewers should still be aware of these common issues.

What if a reviewer is consistently slow or overly critical?

Set clear team expectations about review turnaround time (for example, within 24 hours). If someone is slow, a gentle ping is appropriate. For overly critical reviews, consider having a conversation about feedback style. Many people don't realize how their comments land until it's pointed out. Team retrospectives are a good place to discuss review culture.

Can I merge a PR with unresolved comments?

If comments are suggestions (not required changes) and there's an approval, yes. However, all threads should be resolved or acknowledged before merging. Leaving unresolved comments creates confusion about whether the feedback was addressed. Use the "resolve conversation" button when a thread is complete.

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Great code reviews build great code and great teams.