What Is a Code Review?

A code review is the practice of having one or more peers examine a proposed change before it is merged into the shared codebase.

Code review is where a human pair of eyes complements the automated checks of CI. Before a change becomes part of the main codebase, a teammate reads it, asks questions, and gives feedback, catching issues that tools cannot and spreading knowledge across the team.

What it is

In a code review, the author proposes a change, usually as a pull request, and a reviewer reads the diff, considers correctness, clarity, and design, and either approves it or requests changes. It is a deliberate quality gate that happens before the change merges.

How the process works

The author opens a pull request describing the change.
CI runs automated checks: build, tests, linting.
A reviewer reads the diff and leaves comments.
The author addresses feedback with follow-up commits.
Once approved and checks pass, the change is merged.

An example

A developer opens a pull request adding a caching layer. CI confirms the tests pass, and a reviewer notices the cache is never invalidated when data changes, a subtle bug no test covered. The author fixes it, the reviewer approves, and a future production incident is avoided.

Why reviews improve quality

Reviewers catch logic errors, unclear code, missing tests, and design problems that automated checks miss. Just as importantly, reviews spread understanding: more than one person now knows how the change works. They also nudge authors toward clearer code, since they know it will be read.

Working well with CI

Automated checks and human review divide the labor. CI handles the mechanical, tireless work, does it build, do tests pass, is it formatted, so reviewers can focus on judgment: is this the right design, is it correct, is it maintainable. Together they form a strong gate before merge.

Key takeaways

Code review has peers examine a change before it merges.
It catches issues tools miss and spreads team knowledge.
It pairs with CI: machines check mechanics, humans judge design.