Git Bisect: Finding the Commit That Broke Everything

In this tutorial, you'll learn about Git Bisect: Finding the Commit That Broke Everything. We cover key concepts, practical examples, and best practices.

Git bisect performs a binary search through commit history to find the exact commit that introduced a bug in log2(N) steps instead of checking every commit manually.

In this tutorial, you'll learn Git bisect — a powerful tool that uses binary search to find the exact commit that introduced a bug. Instead of manually checking dozens of commits, bisect narrows it down in logarithmic time. By the end, you'll run manual and automated bisect sessions and integrate bisect into your debugging workflow.

flowchart TD
  A[Mark bad commit: HEAD] --> B[Mark good commit: old known-working]
  B --> C[Bisect: checkout middle commit]
  C --> D{Test the commit}
  D -->|Good| E[Mark as good]
  D -->|Bad| F[Mark as bad]
  E --> G{More commits?}
  F --> G
  G -->|Yes| C
  G -->|No| H[Found first bad commit]

Starting a Bisect Session

# Start bisect
git bisect start

# Mark current HEAD as broken
git bisect bad

# Mark a known-good commit (e.g., from a tag)
git bisect good v1.0.0

Expected output:

Bisecting: 8 revisions left to test after this (roughly 3 steps)
[c3a2b1f] Add login feature

Git checks out a commit midway through history for you to test.

Testing Each Step

At each bisect step, test whether the bug exists:

# If the bug is present:
git bisect bad

# If the bug is not present:
git bisect good

Git continues narrowing down:

Bisecting: 4 revisions left to test after this (roughly 2 steps)
[9d8e7f6] Update API endpoint

After a few more steps:

c1b2a3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9 is the first bad commit
commit c1b2a3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9
Author: Developer Name
Date:   Mon Jun 15 14:30:00 2026 +0000

    Fix login bug

Automated Bisect

For bugs with automated tests, let Git run bisect automatically:

git bisect start HEAD v1.0.0
git bisect run npm test

Or with a custom script:

git bisect start HEAD v1.0.0
git bisect run python -m pytest tests/test_login.py

Expected output:

running  python -m pytest tests/test_login.py
running  python -m pytest tests/test_login.py
c1b2a3d4e5f6g7h8i9j0k1l2m3n4o5p6q7r8s9 is the first bad commit

The git bisect run command automates the entire process. Your script or test command must exit with 0 for "good" and non-zero for "bad".

Bisect with Skip

Some commits may be untestable (merge commits, broken builds). Skip them:

git bisect skip

Or skip a range of commits:

git bisect skip a1b2c3d..e5f6g7h

Visualizing Bisect Progress

git bisect log

Expected output:

git bisect start
# bad: [a1b2c3d] Latest commit
git bisect bad a1b2c3d
# good: [e5f6g7h] Release v1.0
git bisect good e5f6g7h
# good: [b3c4d5e] Add config file
git bisect good b3c4d5e
# first bad commit: [c1b2a3d] Fix login bug
git bisect bad c1b2a3d

Ending a Bisect Session

git bisect reset

This returns your working directory to the original branch.

Common Errors

Practice Questions

Challenge

Create a repository with 20 commits. Introduce a bug in commit 12. Use git bisect to find the exact commit that introduced the bug. Then write a Python script that reproduces the bug and use git bisect run to automate the search. Verify you found the correct commit.

Real-World Task

In a production application, a bug was introduced sometime in the last 50 commits. Write an automated test that reproduces the bug. Use git bisect run with that test to identify the exact commit. Once found, use git revert to create a fix commit. Push the fix and the revert. This binary search technique is regularly used at DodaTech when debugging Durga Antivirus Pro's scanning engine across hundreds of commits.

Built by the developers of Doda Browser, DodaZIP, and Durga Antivirus Pro.