Imagine a retrospective where no one mentions “the bug that slipped through.” According to Stack Overflow’s 2024 survey, unreviewed code is one of the top sources of technical-debt anxiety. That’s why code reviews come into the picture. They catch problems early, reduce tech debt, and keep teams aligned. This guide explains where reviews originate, why they matter, when to raise alerts, and how authors can set up better Pull Requests (PRs). It also shows reviewers what to look for, turning every review into an investment in quality, team growth, and smoother releases.

What are Code Reviews?

A code review is an engineering practice in which another team member (different from the author) reviews your code changes before accepting them into the main codebase.

The Origin of Code Reviews

Code review has been around for a long time. Decades ago, engineers started reviewing printed code in person. In 1976, IBM’s Michael Fagan formalized this with a process called “Fagan Inspections,” focusing purely on finding errors without discussion. Early email patch threads gave way to tools like Google’s Mondrian in 2006, which brought more structure and made reviews easier to scale. Git and GitHub then popularized the PR workflow, turning reviews into an everyday habit for developers everywhere. 

Why are Code Reviews Important?

Code reviews help spot problems early, improve code quality, and create better alignment across teams. Beyond the technical benefits, they also shape how teams communicate and collaborate.

Here are all the reasons why they matter:

  • Catch bugs early: Reviews surface issues before they reach production, often detecting 55-80% of problems missed by the original author.
  • Improve code quality: Developers tend to write cleaner, more efficient code when they know someone else will review it.
  • Promote consistency: Code reviews help keep the codebase consistent by encouraging authors to follow standard naming conventions and style guides.
  • Encourage knowledge sharing: Reviewers get exposure to different parts of the code. Authors learn from the reviewer’s suggestions and experience.
  • Keep the team aligned: Reviews give everyone visibility into ongoing changes.
  • Build team culture: They create opportunities for constructive feedback and recognition, establishing a sense of ownership and accountability.
  • Boosts confidence through recognition: Praising well-written code during reviews builds the author’s confidence. It shows the developers that their work is valued and motivates them to keep improving.
  • Compliance: Reviews support compliance by creating documented records required for audits, certifications, and regulatory checks.
  • Make code easy to scale: Clear code helps reviewers understand it quickly, making it easier for future authors to build on safely. That's why code reviews are key to long-term scalability.

Which Code Changes Require a Review?

Not every code change needs the same level of scrutiny. The decision to review depends on the team’s goals and risk tolerance. Some teams require code reviews on every PR. Others apply judgment based on the change size or impact.

Here are some approaches:

  • Review all PRs: Common in larger teams or regulated environments, where traceability and accountability matter.
  • Skip trivial changes: Teams usually allow minor, low-risk changes to bypass the review process, like fixing spelling errors, updating comments, adjusting formatting, or making small configuration tweaks that don't impact how the software runs.
  • Use team-defined rules: Teams often set their own thresholds based on experience. For example, changes under a certain number of lines or touching non-critical files might be exempt.
  • Rely on trust and context: In fast-moving teams, experienced developers often review their own minor changes and send bigger updates for peer review.

Code Author Responsibilities Before a Review

Good reviews start with good PRs. The easier a change is to read and understand, the faster it gets reviewed and the better is the feedback. Authors can make this easier by following a few basic principles before requesting a review.

  • Limit the scope: A PR should focus on one clear task. Don’t bundle unrelated changes in the same update.
  • Smaller PRs are better: Large PRs take more effort to review, and reviewers often end up rubberstamping them without reviewing everything. To avoid this, many teams like Meta and LinkedIn recommend keeping PRs under 200-400 lines of code. 
  • Test before submitting: Make sure the change works as expected and doesn’t break existing functionality.
  • Separate refactors from logic changes: Mixing refactors and logic changes makes it harder to understand what to focus on during review.
  • Write a clear description: Clearly explain what the change does, why it was made, and what the reviewer should focus on. A good description reduces confusion and speeds up the review process.

Who Should Do the Code Reviews?

The right reviewer depends on the nature of the change. In most cases, the code author suggests a teammate who knows the relevant part of the codebase. This makes sure the review is both technically accurate and that the reviewer is aware of the broader context.

For important or sensitive changes, a senior engineer or tech lead typically steps in. Their experience helps catch deeper issues that might go unnoticed in a routine review. When the change is large or touches multiple systems, teams often bring in more than one reviewer to cover different areas of expertise.

Choose a reviewer who can judge the code for both correctness and long-term maintainability, not just someone who’ll just give a quick approval.

Code Reviewer Responsibilities While Performing the Review

A good code review checks if the change meets its goal, fixing a bug or adding a feature. The code should be readable, well-structured, and follow the project’s style. Watch for duplication that could be replaced with existing utilities. Make sure tests are clear and cover the right cases, including key integrations.

  • Functional Correctness and Logic: Ensure that the code delivers the intended outcome while gracefully handling unexpected conditions.
  • Code Clarity and Readability: Check whether the code is easy to follow with clean structure, self-explanatory naming conventions, and purposeful comments.
  • Performance: Make sure that the code runs efficiently, reduces unnecessary computation, minimizes I/O, and manages parallel execution safely.
  • Security: Check if the code is secure by checking inputs, securing credentials, controlling permissions, and avoiding risky dependencies.
  • Testing and Observability: Verify that the code is well-tested across edge cases and integrates logs to support post-release debugging.
  • Maintainability: Ensure that the code is modular, easy to change/update, well-documented, and free of duplication to support long-term development.

Conclusion

A well-run code review delivers long-term value across the board. It catches over half of the hidden bugs before they reach production and avoids the high cost of late-stage fixes. When reviewers come from different teams or backgrounds, they bring broader insights and help spread knowledge across the organization. Use this guide in your PR process, automate the basics, and treat every review as the last checkpoint before well-structured and reliable code ships.