We do line-by-line code reviews of all changes (high-assurance software, so we have to - but it's worth it anyway.) Some kind of tool is useful, since it allows

We do line-by-line code reviews of all changes (high-assurance software, so we have to - but it's worth it anyway.) Some kind of tool is useful, since it allows you to (a) review code on your own schedule, and (b) stores the comments (for later review, if someone is on holiday, so that you can refer back to your initial comment when reviewing an improvement, ...) That said, code reviewing is a skill (and perhaps a talent), and not the same skill as software development; a degree of training - if just internal and informal - is necessary. Thorough code reviews take a significant fraction of the effort needed to write the code in the first place; direct tooling costs are going to be insignificant in comparison. (And note that e.g. Gerrit and even GitHub both offer some degree of free tooling.)