Git Bisect

Bisect performs a binary search through your commit history to find which commit introduced a bug. Instead of checking each commit one-by-one, it halves the search space at every step.

Manual bisect

$ git bisect start
$ git bisect bad                    # current commit has the bug
$ git bisect good <hash>            # this older commit was fine

Git checks out a midpoint commit. Test it, then mark it:

$ git bisect good                   # midpoint is clean
$ git bisect bad                    # midpoint has the bug

Repeat until Git identifies the first bad commit, then clean up:

$ git bisect reset                  # return to original branch

Automated bisect with a test script

If you have a script that exits 0 for good and non-zero for bad, bisect can run unattended:

$ git bisect start HEAD <good-hash>
$ git bisect run ./test.sh

Git runs the script at each midpoint and reports the first bad commit when done.

Tips

The good and bad commits do not have to be on the same branch — bisect works across the entire reachable history.
If a midpoint commit cannot be tested (e.g. broken build), use git bisect skip to move past it.
Use git bisect log to replay or share a bisect session.

For blame, log search, and other debugging tools, see the Debugging recipe.