Often when something is broken, it’s because of a recent change. Usually I look at recent changes manually, but git bisect is an amazing tool for finding exactly which git commit caused the problem.

We don’t have space for a full git bisect tutorial here, but here’s how you start using it:

git bisect start   
git bisect bad HEAD   
git bisect good 1fe9dc 

(1fe9dc is the ID of a commit that doesn’t have the bug)

Then you can either tag buggy commits manually or run a script that does it automatically.