Software Engineering at Google

Chapter 9. Code Review

Written by Tom Manshreck and Caitlin Sadowski

Edited by Lisa Carey

Code review is a process in which code is reviewed by someone other than the author, often before the introduction of that code into a codebase. Although that is a simple definition, implementations of the process of code review vary widely throughout the software industry. Some organizations have a select group of “gatekeepers” across the codebase that review changes. Others delegate code review processes to smaller teams, allowing different teams to require different levels of code review. At Google, essentially every change is reviewed before being committed, and every engineer is responsible for initiating reviews and reviewing changes.

Code reviews generally require a combination of a process and a tool supporting that process. At Google, we use a custom code review tool, Critique, to support our process.¹ Critique is an important enough tool at Google to warrant its own chapter in this book. This chapter focuses on the process of code review as it is practiced at Google rather than the specific tool, both because these foundations are older than the tool and because most of these insights can be adapted to whatever tool you might use for code review.

Note

For more information on Critique, see Chapter 19.

Some of the benefits of code review, such as detecting bugs in code before they enter a codebase, are well established² and somewhat obvious (if imprecisely measured). Other benefits, ...