Google Code Review Practices: Guidelines and Principles

Google recently published an engineering practice document that details code review (CR) guidelines, explaining the roles of reviewers, authors, and change lists, and emphasizing the goal of continuously improving code quality.

1. CR Standards

Reviewers must balance encouraging progress with maintaining high standards, focusing on design, functionality, complexity, testing, naming, comments, style, documentation, and overall system impact.

2. What to Look for in a CL

Key areas include overall design, functional correctness, complexity (avoiding over‑engineering), adequate testing, clear naming, purposeful comments (explaining why), adherence to style guides, updated documentation, line‑by‑line review, and appropriate expertise for security or concurrency concerns.

3. How to Browse a CL

Start with a high‑level view of the change description, identify the core files, then review remaining changes in a logical order, optionally reviewing tests first to understand expected behavior.

4. Review Speed

Fast reviews improve team velocity; reviewers should respond within a workday, prioritize quick feedback, avoid unnecessary interruptions, and use LGTM approvals when appropriate. Large changes should be split into smaller CLs.

5. Writing Review Comments

Provide constructive, polite feedback, explain disagreements, highlight positives, and suggest alternatives. When conflicts arise, seek consensus through discussion or escalation. Avoid over‑optimizing speed at the expense of quality.

6. Summary

Effective code review requires clear standards, thorough yet efficient examination of changes, respectful communication, and continuous improvement to maintain a healthy codebase.