December 3, 2023
What Is Code Review

Code review, also known as peer code review, is the deliberate and methodical gathering of one’s fellow programmers to examine each other’s code for errors. It has been consistently demonstrated that code review may speed up and simplify the software development process, unlike a few other techniques. Software and methods for peer code review exist, but it’s crucial to comprehend the idea behind it. Software is created by people. As a result, the software is frequently filled with errors. This is a clear association because it is human nature to make mistakes. But why software engineers frequently omit using that other great talent of human nature—the capacity to see—in favor of manual or automated testing to validate their code is less evident.

You risk missing out on the great advantages of code reviews or code inspections if you’re a software development manager or a hands-on programmer. Peer reviews can streamline the development process and significantly cut down on the amount of work later on that needs to be done by the QA teams when done properly. Reviews can also save you money, particularly by catching the kinds of bugs that might get past testing and production, and onto end-users laptops (whereupon those irate customers will post scathing reviews of your product on Amazon or in the App Store and your sales will suffer accordingly).

But while reducing costs and saving time are important considerations in the software development industry, code reviews can offer some additional, more human-centric ROI. Workplaces that encourage programmers to discuss their code with one another tend to promote greater communication and camaraderie, distribute the sense of “ownership” for any piece of code, and offer junior developers an invaluable educational context by demonstrating better ways to write clean code through real-world examples, solve common problems with helpful shortcuts, and visually identify any number of potential trouble spots, such as memoization.

Managing the lifecycle of digital files outside of the source code is made simpler for an organization by document review.

If a development team isn’t currently doing so, the combination of these criteria should motivate them to do so (especially in light of the statistics). Would a reputable book publisher, after all, risk printing thousands of copies of an author’s work without first having a team of editors read and copyedit the manuscript? The same reasoning holds true for software creators and distributors. Now, though, with ever-shorter production cycles, where does one start?

Understanding Code Review

The Email Thread

A particular piece of code is sent to the appropriate coworkers through email as soon as it is prepared for review, so they can individually review it as soon as their workflow permits. While this method can be more adaptable and flexible than more conventional approaches, such as collecting five people in a room for a code-inspection meeting, an email thread of suggestions and divergent opinions has a tendency to become confusing very quickly, leaving the original coder to sort through it all.

Pair Programming

One of the ideas of Extreme Programming (XP) is the pairing of developers to work on the same piece of code simultaneously, verifying each other’s work as they go. This method of building software puts developers side by side (at least metaphorically). It appears to integrate code review directly into the programming process and provides senior developers with a useful way to mentor their less experienced peers. Other forms of code review, however, might offer greater objectivity because writers and even co-authors often feel too connected to their own work. Additionally, pair programming can require more workers and time than alternative approaches.


The over-the-shoulder method is one of the oldest, simplest, and most natural ways to participate in peer code review, and is more comfortable for most engineers than XP’s pair programming. Once your code is complete, simply ask a knowledgeable coworker to examine it while you explain why you developed it that way. You can sit down at their workstation or visit theirs. This informal strategy is undoubtedly “lightweight,” but if it doesn’t have any ways of tracking or documenting, it might even be a touch too light. Bring a notepad, as a hint.


We kept our personal favorite for last because, in our opinion, there isn’t a more straightforward or effective approach to reviewing code than with software-based code review tools, some of which are browser-based or naturally interact with a wide range of common IDE and SCM development frameworks. Software tools enable reviews to happen asynchronously and non-locally, sending notifications to the original coder when new reviews come in, and keeping the whole process moving efficiently with no meetings and no one having to leave their desks to contribute. These features overcome many of the limitations of the preceding approaches above. The ability to examine and edit requirements documents is another feature of some systems. More importantly, they can also produce important usage data, which provides the audit trials and review metrics required for process improvement and compliance reporting.

Tracking Your Progress

It goes without saying that metrics are important in the world of code review, especially since so many dev teams out there are still waiting to be persuaded about its eventual efficacy as a regular practice. However, there is no better way to justify, and most intelligently utilize, the time and brainpower required, than tracking actual metrics. This is why some existing studies are so instructive, like a 2005–2006 analysis of Cisco’s peer–code review process carried out by SmartBear Software, which surveyed no less than 2,500 reviews of 3,200,000 lines of code written by 50 developers. The outcome? The metrics (taken from such a huge sample set) allowed the researchers to gain the following critical insights about code review in general. Not only was it found that Cisco’s code review method recognized considerably more problems, or defects than routine testing alone could have discovered.

  • Less than 200 lines of code (LOC) should be under review, and no more than 400 should be, as anything more than that overwhelms reviewers and they cease finding errors.
  • The optimum fault detection rates are fewer than 300 LOC/hour for inspection rates, and rates under 500 are still good but anticipate missing a considerable portion of defects if LOC is reviewed more quickly than that.
  • The reviews written by authors that provide annotations and explanations are much less flawed than those who do not. The cause is probably because authors are compelled to evaluate their own code.
  • The entire review duration should be no more than 90 minutes and no less than 60 minutes. After 90 minutes of inspection, the likelihood of defects is much reduced.
  • 15 defects should be expected per hour.

The Future of Peer Code Review

Code review is simply one part of any software production team’s Quality Assurance plan, despite the fact that we have been highlighting it throughout this article. Static analysis and the many different types of testing complete the QA checklist. However, it’s a crucial part since it frequently eliminates bugs as soon as they hatch, before they have a chance to develop into large, unmanageable creatures, as well as identifies “hidden” bugs that might not be an issue right away but could prevent the product from evolving in the future.

Unit tests are always useful for determining whether a given function “works” as intended, but code review can reveal subtler problems that are better suited to human perception—such as scalability, error handling, and basic legibility (including the written clarity of developers’ annotations and requirements docs). It appears likely that tool-assisted peer code review will eventually replace the previous “lightweight” forms as the most appropriate and inclusive methodology available, just as test automation has evolved to become more complex and the testing teams’ preferred tool.

It only makes it natural that there will be a growing reliance on the appropriate digital tools in a world where software production schedules are quickening, continuous deployment is becoming the standard, and customer feedback is a never-ending feedback loop. Github effects on code review can be seen in the rise of real reviews performed by development teams.
However, even in ten or twenty years, unless new software miraculously begins to write itself, we can be sure that the mainstay of peer code reviews—namely, people—will continue to take the lead. Indeed, as long as people are reviewing code, code will continue to get better even in the absence of software review tools since human psychology is what drives code improvement.

The Importance of Code Review

  1. Bug Detection and Prevention: Code review provides an additional layer of defense against potential bugs and programming errors. By having fresh eyes review the code, developers can identify logic flaws, syntax errors, and potential issues early in the development cycle, reducing the chances of defects making their way into the final product.
  2. Knowledge Sharing and Collaboration: Code review encourages knowledge sharing among team members. Developers can learn from each other’s coding styles, best practices, and domain expertise, leading to a more skilled and cohesive team. Additionally, code review fosters a collaborative environment where team members can openly discuss solutions and alternative approaches.
  3. Maintaining Coding Standards: Consistent coding standards are essential for maintaining a clean and maintainable codebase. Code review enforces adherence to these standards, ensuring that the code remains readable, well-structured, and scalable. This consistency simplifies maintenance and future development efforts.
  4. Improving Software Quality: High-quality code is the foundation of robust and reliable software. Code review allows developers to catch and rectify issues before they impact end-users, resulting in a more stable product that meets customer expectations.
  5. Risk Reduction: Identifying and fixing issues early in the development process reduces project risks. Code review minimizes the likelihood of encountering severe bugs later in the software lifecycle, saving time and effort that would have otherwise been spent on debugging and fixing issues.

Best Practices for Code Review

  1. Set Clear Objectives: Establish clear objectives and guidelines for code review. Define what aspects team members should focus on, such as security, performance, or coding standards, to ensure consistent and targeted reviews.
  2. Encourage Constructive Feedback: Promote a positive and constructive review culture. Encourage reviewers to provide feedback in a respectful manner, focusing on the code’s improvement rather than criticizing the developer.
  3. Automate Code Review (Linting): Incorporate automated code analysis tools and linters to identify common issues automatically. This helps streamline the review process and ensures that basic coding standards are met before human reviewers step in.
  4. Rotate Reviewers: Rotate the individuals responsible for code reviews to avoid bias and encourage knowledge sharing. Different perspectives can lead to more comprehensive assessments of the codebase.


In conclusion, code review is an indispensable practice in software engineering that helps teams maintain high-quality, reliable, and maintainable codebases. By catching bugs early, adhering to coding standards, and fostering collaboration among team members, code review plays a vital role in ensuring successful software development projects. Embracing code review as a standard practice empowers software engineers to create robust applications that meet users’ needs and exceed expectations.

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