git bisect: find the commit that broke production in minutes, not days
Your CI was green last Friday. Today, the payments test is failing. Somewhere between Friday's merge and now, 47 commits landed on main . Which one broke it? Most developers answer this the wrong way: they scroll through git log , check out suspicious commits one by one, and run the test manually. An hour later, they're still guessing. There's a command built for this exact problem. It's called git bisect , and once you learn it, you'll never debug regressions the old way again. How bisect works git bisect is a binary search across your commit history. You tell Git two things: A good commit (a known point where the bug didn't exist) A bad commit (a known point where the bug exists — usually HEAD ) Git then checks out the commit halfway between them. You test. You mark it as good or bad. Git narrows the range by half. Repeat. With 47 commits between "good" and "bad", it takes at most 6 steps (log₂ 47) to find the exact commit that introduced the bug. Versus checking every commit manually, that's the difference between 5 minutes and an hour. The manual workflow # Start a bisect session $ git bisect start # Mark the current state (HEAD) as bad $ git bisect bad # Mark a known-good commit $ git bisect good a3f1d22 # Bisecting: 23 revisions left to test after this (roughly 5 steps) # [7e4b9c1] refactor: extract payment validator # Git has checked out a commit in the middle. Run your test. $ npm test -- --grep "payments" # Test passed — mark this commit as good $ git bisect good # Bisecting: 11 revisions left to test after this (roughly 4 steps) # [b2d8e11] feat: add retry logic to payment API # Test failed — mark this commit as bad $ git bisect bad # ... continue until Git announces the first bad commit: # b2d8e11 is the first bad commit # commit b2d8e11 # Author: leo@company.com # Date: Tue Apr 15 11:42:03 # feat: add retry logic to payment API # Done — reset to where you started $ git bisect reset In 6 commands, you know exactly which commit broke the tests. No guessing