The command takes various subcommands, and different options depending on the subcommand:

This command uses a binary search algorithm to find which commit in your project’s history introduced a bug. You use it by first telling it a "bad" commit that is known to contain the bug, and a "good" commit that is known to be before the bug was introduced. Then git bisect picks a commit between those two endpoints and asks you whether the selected commit is "good" or "bad". It continues narrowing down the range until it finds the exact commit that introduced the change.

In fact, git bisect can be used to find the commit that changed any property of your project; e.g., the commit that fixed a bug, or the commit that caused a benchmark’s performance to improve. To support this more general usage, the terms "old" and "new" can be used in place of "good" and "bad", or you can choose your own terms. See section "Alternate terms" below for more information.

Eventually there will be no more revisions left to inspect, and the command will print out a description of the first bad commit. The reference refs/bisect/bad will be left pointing at that commit.

Keep repeating the process: compile the tree, test it, and depending on whether it is good or bad run git bisect good or git bisect bad to ask for the next commit that needs testing.

You should now compile the checked-out version and test it. If that version works correctly, type

Once you have specified at least one bad and one good commit, git bisect selects a commit in the middle of that range of history, checks it out, and outputs something similar to the following:

As an example, suppose you are trying to find the commit that broke a feature that was known to work in version v2.6.13-rc2 of your project. You start a bisect session as follows:

For example, git bisect reset bisect/bad will check out the first bad revision, while git bisect reset HEAD will leave you on the current bisection commit and avoid switching commits at all.

With an optional argument, you can return to a different commit instead:

By default, this will return your tree to the commit that was checked out before git bisect start . (A new git bisect start will also do that, as it cleans up the old bisection state.)

After a bisect session, to clean up the bisection state and return to the original HEAD, issue the following command:

Alternate terms

Sometimes you are not looking for the commit that introduced a breakage, but rather for a commit that caused a change between some other "old" state and "new" state. For example, you might be looking for the commit that introduced a particular fix. Or you might be looking for the first commit in which the source-code filenames were finally all converted to your company’s naming standard. Or whatever.

In such cases it can be very confusing to use the terms "good" and "bad" to refer to "the state before the change" and "the state after the change". So instead, you can use the terms "old" and "new", respectively, in place of "good" and "bad". (But note that you cannot mix "good" and "bad" with "old" and "new" in a single session.)

In this more general usage, you provide git bisect with a "new" commit that has some property and an "old" commit that doesn’t have that property. Each time git bisect checks out a commit, you test if that commit has the property. If it does, mark the commit as "new"; otherwise, mark it as "old". When the bisection is done, git bisect will report which commit introduced the property.

To use "old" and "new" instead of "good" and bad, you must run git bisect start without commits as argument and then run the following commands to add the commits:

git bisect old [<rev>]

to indicate that a commit was before the sought change, or

git bisect new [<rev>...]

to indicate that it was after.

To get a reminder of the currently used terms, use

git bisect terms

You can get just the old (respectively new) term with git bisect terms --term-old or git bisect terms --term-good .

If you would like to use your own terms instead of "bad"/"good" or "new"/"old", you can choose any names you like (except existing bisect subcommands like reset , start , …​) by starting the bisection using

git bisect start --term-old <term-old> --term-new <term-new>

For example, if you are looking for a commit that introduced a performance regression, you might use

git bisect start --term-old fast --term-new slow

Or if you are looking for the commit that fixed a bug, you might use

git bisect start --term-new fixed --term-old broken