Definition
Code review is a teamwork process where fellow developers read through the source code a developer wrote, look for errors, and help raise its quality. It catches logic flaws that are easy to miss alone, and it's the most common development practice for lifting the quality of a whole team's software.
Why Read Together Instead of Checking Alone?
You've probably had this happen. You reread something you wrote three or four times and see no typos, but the moment you show it to a friend, they spot one right away. That's because when you read your own writing, your brain follows the intention in your head and skips right over the mistakes.
Programming works the same way. Code you wrote yourself tends to have cognitive blind spots. You get so used to the flow of your own logic that you walk right past serious errors and unusual situations.
A coworker's eyes are a good mirror for lighting up those blind spots. Looking at the code with fresh eyes, they see gaps clearly: "What if the user leaves the field blank? Will it crash?" or "What happens if the internet connection drops?" In the end, code review puts up a sturdy safety net before errors reach the real service.
It's Not Just About Catching Bugs
It's easy to think of code review as just an inspection to find what's wrong. But in real development work, code review is also a great place for the whole team to share knowledge and grow together.
Experienced senior developers can naturally pass on tips for writing cleaner, more efficient code, along with good practices from the industry. In turn, junior developers learn new techniques and design approaches just by reading their seniors' and teammates' code carefully.
It also means everyone on the team gets to know each other's code. If only one person understands a certain feature, nobody can fix the system when that person goes on vacation or leaves the company. With steady code review, you end up with an environment where anyone on the team can maintain the system.
A Bit More Precisely
To put it more precisely, code review is not a test of the author's skill. It's a collaborative process for making a program sturdier.
A healthy review culture comes from focusing on the logic of the code itself, not on emotional criticism aimed at a person. For example, instead of asking, "Why did you write this so inefficiently?", it's better to give a specific reason and an alternative: "Written this way, the server could slow down when lots of users show up. How about trying a different function?"
Today, many IT companies do code review online every day, using the pull request feature of collaboration services like GitHub. Your code only gets merged into the final program after your teammates have looked it over carefully and approved it. This process protects the quality and stability of the service in a systematic way.
Common misconceptions
Code review is an inspection only for beginner developers who aren't skilled enough.
On teams that do code review, even veteran developers with lots of experience have their code reviewed by teammates in the same way. Anyone can have blind spots or make mistakes regardless of skill, and it matters much more that the whole team shares the code.
Where you meet it
After building a new payment feature, you ask teammates for a code review, and together you check that there's no risk of charging the payment amount twice.
A teammate says a variable name is too vague, so you rename it to something clear that's easier for other people to read later.
In one sentence
Code review is a teamwork process where colleagues read code together, catch errors early, and raise the quality of the whole team's software.