In doing a code review, you should make sure that: The code is well-designed. The functionality is good for the users of the code. Any UI changes are sensible and look good. Any parallel programming is done safely. The code isn’t more complex than it needs to be. The developer isn’t implementing things they might need in the future but don’t know they need now. Code has appropriate unit tests. Tests are well-designed. The developer used clear names for everything. Comments are clear and useful, and mostly explain why instead of what. Code is appropriately documented (generally in g3doc). The code conforms to our style guides. You can have more detail at https://google.github.io/eng-practices/review/reviewer/looking-for.html