What is a code review?

Code review: definition and purpose

In a code review, a second developer reads a colleague’s changes before they reach the main version. It is the four-eyes principle for software. What gets checked is function, readability, security and consistency with the project’s standards: does the code solve the task, and can someone still understand and change it a year from now?

The side effect matters: reviews spread knowledge. When several people know every change, the project does not hang on a single developer. They are also an opportunity to enforce standards together and guide newcomers. Clients benefit indirectly through fewer errors in operation.

How a code review works

The usual process runs through pull requests or merge requests on Git platforms such as GitHub or GitLab. The developer describes the change, colleagues comment line by line, request adjustments or approve the change. Only after approval is it merged into the main branch.

Automated checks run in addition: linters verify style and typical error patterns, tests secure the behavior, static analysis looks for security problems. That way, people do not have to argue about indentation and spaces and can concentrate on logic, architecture, security and risks, where their judgment is really needed.

Real-world example: discount calculation in an online store

A retailer has tiered discounts for business customers built into its store. The developer implements the calculation, and in the review the colleague notices that rounding is wrong for certain quantities and that the discount accidentally also applies to shipping costs. Neither is in the task description.

Both would probably have slipped through spot checks and only been noticed through customer complaints. This way, the correction is made before release, and no customer ever sees a wrong total. For payment functions, permission checks and interfaces to accounting systems too, a second look is especially worthwhile, because errors there are expensive.

Benefits, limits and common mistakes

Code reviews raise quality and security and improve collaboration. But they cost time and are only as good as the care of the reviewers; they replace neither tests nor business acceptance. They can also slow teams down if approvals sit for days. Typical mistakes:

• Reviewing huge changes all at once, so they are only skimmed
• Waving changes through without a real review to keep to the schedule
• Discussing only style issues instead of logic and security
• Criticizing the person instead of the code, which strains collaboration
• No rules on what a review must check

What businesses should look out for

Ask providers whether every change is checked by a second person and what automated checks run in addition. Critical areas such as payment, login and data access deserve special attention. At Nano Concepts, every change goes through a review and automated checks before it reaches your system.