What is Code Review and When Is It Needed?

You can write code. You can edit existing code. You can even rewrite it from scratch. There’s a lot you can do with code. But what’s the point if the code lives in its own echo chamber? If the same person writes, views, and edits it, many critical errors can drift from one version to another unnoticed without external evaluation. Code locked within the confines of a single text editor is highly likely to stagnate, accumulating inefficient constructs and architectural decisions, even if written by an experienced developer.

This is why every developer should understand what code review is, how it’s done, and what tools are needed. Presenting your code properly to others, gathering feedback, and making changes wisely is important. Only this way can code remain “fresh” and efficient, and applications based on it — secure and high-performing.

Code review is the process of examining code by one or more developers to identify errors, improve quality, and increase readability.

Types of Code Review

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1. Formal Review

A formal review is a strict code-checking process with clearly defined stages. It’s used in critical projects where errors can have serious consequences — for example, in finance or healthcare applications. The analysis covers not just the code but also the architecture, performance, and security. Reviewers often include not just developers but also testers and analysts.

For example, a company developing a banking app might follow these steps:

• Development: A developer completes a new authentication module and submits a pull request via GitHub.
• Analysis: A review group (2 senior developers + 1 security specialist) is notified and checks the code for logic, readability, and security (e.g., resistance to SQL injection and XSS attacks).
• Discussion: Reviewers meet the developer over Zoom and give feedback.
• Documentation: All notes are posted in GitHub comments and tracked in Jira. For instance, some RESTful requests may be flagged as vulnerable with a recommendation to use parameterized queries.
• Fixes: The developer updates the code and the pull request; the cycle repeats until approval.
• Approval: Once reviewers are satisfied, the code is merged into the main branch.

2. Informal Review

Informal code review is less strict and more flexible, usually involving:

• Quick code discussions in chat or meetings
• Showing code to a colleague in person
• Asking an expert a technical question

This kind of review happens often in day-to-day work and is characterized by spontaneity, lack of documentation, informal reviewer choice, and shallow checks.

In simpler terms, it’s more like seeking advice than a formal third-party audit. It's a form of knowledge sharing.

Types include:

• Over-the-Shoulder Review: One developer shows their code to another in real time (via screen share, chat message, or simply turning the monitor).
• Ad-hoc Review: A developer sends code to a colleague asking them to check it when convenient, e.g., I wrote this handler, but there’s an error. Can you take a look?
• Unstructured Team Review: Code is discussed at a team meeting, casually and collaboratively, often with knowledge sharing.

Feedback is given as recommendations, not mandates. Developers can ignore or reject suggestions.

Although informal reviews are less reliable than formal ones, they’re quicker and easier, and often complement formal reviews.

Examples of integration:

• Preliminary Checks: Before a pull request, a dev shows code to a colleague to discuss and fix issues.
• Informal Discussion During Formal Review: Reviewers may chat to resolve issues more efficiently.
• Quick Fixes: Developers make changes right after oral feedback instead of long comment exchanges.

3. Pair Programming

Pair programming is when two developers work together on one machine: one writes code, and the other reviews it in real-time.

It’s literally simultaneous coding and reviewing, which helps catch bugs early.

Roles:

• Driver: Writes code, focused on syntax and implementation.
• Navigator: Reviews logic, looks for bugs, suggests improvements, and thinks ahead.

Roles can be switched regularly to keep both engaged.

Variants:

• Strong Style: Navigator makes decisions, and the driver just types. It works well if one of the developers is more experienced.
• Loose Pairing: Both share decision-making, swapping roles as needed.

Though rare, pair programming has advantages:

• Instant Feedback: Bugs are fixed immediately.
• In-depth Review: The second dev is deeply involved in writing the code.
• On-the-job Learning: Juniors learn directly from experienced peers.

It’s more of a collaborative development method than a strict review.

4. Automated Review

Automated code review uses tools that analyze code for errors, style, and vulnerabilities without human intervention.

These tools are triggered automatically (e.g., after compilation, commit, or pull request).

They analyze, run tests (e.g., unit tests), and generate reports. Some tools can even auto-merge code if it passes checks.

Automated code review is part of DevOps and is common in CI/CD pipelines before deploying to production.

Types:

• Static Analysis: Checks code without executing it — syntax errors, bad patterns, etc.
• Dynamic Analysis: Runs code to detect memory leaks, threading issues, and runtime errors.

However, for now, tools can't catch business logic or architectural issues. As AI evolves, tools will likely become better at "understanding" code.

When is Code Review Needed?

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Ideally, you should conduct code reviews both in small and large-scale projects.

The only exceptions might be personal side-projects (pet projects), although even these can benefit from outside input.

Automated testing has become standard, from JavaScript websites to C++ libraries.

Still, code review can be skipped for:

• Trivial changes (e.g., formatting, UI text updates)
• Peripheral code (e.g., throwaway scripts, config files)
• Auto-generated code — unless manually modified

In short, review the code only if it plays a critical or central role in the app and a human wrote it.

Main Stages of Conducting Code Review

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Regardless of whether a review is formal, informal, or automated, there are several common stages.

Preparation for Review

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Whether the written code is a new component for a production application or a modification of an existing method in a personal project, the developer is usually motivated to have it reviewed, either by fellow developers or by using automated testing tools.

Accordingly, the developer has goals for the review and a rough plan for how it should be conducted, at least in broad terms.

It’s important to understand who will participate in the review and whether they have the necessary competencies and authority. In the case of automated testing, it’s crucial to choose the right tools.

Otherwise, the goals of the review may not be achieved, and critical bugs might remain in the code.

Time constraints also matter: when all reviewers and testing tools will be ready to analyze the code, and how long it will take. It’s best to coordinate this in advance.

Before starting the actual review, it can also be helpful to self-review—go over the code yourself and try to spot any flaws. There might be problems that can be fixed immediately.

Once the developer is ready for the review, they notify the reviewers via chat, pull request, or just verbally.

Code Analysis and Error Detection

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Reviewers study the code over a period of time. During this process, they prepare feedback in various formats: suggested fixes in an IDE, chat comments, verbal feedback, or testing reports.

The format of the feedback depends on the tools used by the development team, which vary from project to project.

Discussion of Edits and Recommendations

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Reviewers and the developer conduct a detailed discussion of the reviewed codebase.

The goal is to improve the code while maintaining a productive dialogue. For instance, the developer might justify certain controversial decisions and avoid making some changes. Reviewers might also suggest non-obvious improvements that the developer hadn't considered.

Documentation and Task Preparation

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All identified issues should be clearly documented and marked. Based on this, a list of tasks for corrections is prepared. Kanban boards or task managers are often used for this, e.g., Jira, Trello, and GitHub Issues.

Again, the documentation format depends on the tools used by the team.

Even a solo developer working on a personal project might write tasks down in a physical notebook—or, of course, in a digital one. Though keeping tasks in your head is also possible, it’s not recommended.

Nowadays, explicit tracking is better than implicit assumptions. Relying on memory and intuition can lead to mistakes.

Applying Fixes and Final Approval

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Once the list of corrections is compiled, the developer can begin making changes. They often also leave responses to comments.

Bringing code to an acceptable state may take several review rounds. The process is repeated until both reviewers and the developer are satisfied.

It’s crucial to ensure the code is fully functional and meets the team’s quality standards.

After that, the final version of the code is merged into the main branch—assuming a version control system is being used.

Tools for Code Review

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In most cases, code review is done using software tools. Broadly speaking, they fall into several categories:

• Version control systems: Most cloud platforms using version control systems (typically Git) offer built-in review tools for viewing, editing, and commenting on code snippets.
• Collaboration tools: Development teams often use not just messengers but also task managers or Kanban boards. These help with discussing code, assigning tasks, and sharing knowledge.
• Automated analyzers: Each programming language has tools for static code analysis to catch syntax issues, enforce style rules, and identify potential vulnerabilities.
• Automated tests: Once statically checked, the code is run through automated tests, usually via language-specific unit testing libraries.

This article only covers the most basic tools that have become standard regardless of domain or programming language.

GitHub / GitLab / Bitbucket

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GitHub, GitLab, and Bitbucket are cloud-based platforms for collaborative code hosting based on Git.

Each offers tools for convenient code review. On GitHub and Bitbucket, this is called a Pull Request, while on GitLab it’s a Merge Request.

Process:

1. The developer creates a Pull/Merge Request documenting code changes, reviewer comments, and commit history.
2. Reviewers leave inline comments and general feedback.
3. After discussion, reviewers either approve the changes or request revisions.

Each platform also provides CI/CD tools for running automated tests:

• GitHub Actions
• GitLab CI/CD
• Bitbucket Pipelines

These platforms are considered the main tools for code reviews. The choice depends on team preferences. The toolas are generally similar but differ in details.

Crucible

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Atlassian Crucible is a specialized tool dedicated solely to code review. It supports various version control systems: Git, SVN, Mercurial, Perforce.

Crucible suits teams needing a more formalized review process, with detailed reports and customizable settings. It integrates tightly with Jira for project management.

Unlike GitHub/GitLab/Bitbucket, Crucible is a self-hosted solution. It runs on company servers or private clouds.

Pros and cons:

Crucible demands more setup but allows organizations to enforce internal security and data policies.

Other Tools

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Each programming language has its own specialized tools for runtime and static code analysis:

• C/C++: Valgrind for memory debugging
• Java: JProfiler, YourKit for profiling; Checkstyle, PMD for syntax checking
• Python: PyInstrument for performance; Pylint, Flake8 for quality analysis

These tools often integrate into CI/CD pipelines run by systems like GitHub Actions, GitLab CI, CircleCI, Jenkins.

Thus, formal code review tools are best used within a unified CI/CD pipeline to automatically test and build code into a final product.

Best Practices and Tips for Code Review

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1. Make atomic changes

Smaller changes are easier and faster to review. It’s better to submit multiple focused reviews than one large, unfocused one.

This aligns with the “Single Responsibility Principle” in SOLID. Each review should target a specific function so reviewers can focus deeply on one area.

2. Automate everything you can

Automation reduces human error. Static analyzers, linters, and unit tests catch issues faster and more reliably.

Automation also lowers developers’ cognitive load and allows them to focus on more complex coding tasks.

3. Review code, not the developer

Code reviews are about the code, not the person writing it. Criticism should target the work, not the author. Maintain professionalism and use constructive language.

A good review motivates and strengthens teamwork. A bad one causes stress and conflict.

4. Focus on architecture and logic

Beautiful code can still have flawed logic. Poor architecture makes maintenance and scaling difficult.

Pay attention to structure—an elegant algorithm means little in a badly designed system.

5. Use checklists for code reviews

Checklists help guide your review and ensure consistency. A basic checklist might include:

• Is the code readable?
• Is it maintainable?
• Is there duplication?
• Is it covered by tests?
• Does it align with architectural principles?

You can create custom code review checklists for specific projects or teams.

6. Discuss complex changes in person

Sometimes it’s better to talk in person (or via call) than exchange messages—especially when dealing with broad architectural concerns.

For specific code lines, written comments might be more effective due to the ability to reference exact snippets.

7. Code should be self-explanatory

Good code speaks for itself. The simpler it is, the fewer bugs it tends to have.

When preparing code for review, remember that other developers will read it. The clarity of the code affects the quality of the review.

Put yourself in the reviewers’ shoes and ensure your decisions are easy to understand.

Conclusion

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Code review is a set of practices to ensure code quality through analysis and subsequent revisions. It starts with syntax and architecture checks and ends with performance and security testing.

Reviews can be manual, automated, or both. Typically, new code undergoes automated tests first, then manual review—or the reverse.

If everything is in order, the code goes into production. If not, changes are requested, code is updated, and the process is repeated until the desired quality is achieved.