Fixing the last commit

You've just committed, and then you spot a typo in the message. Or a file you forgot to add. You don't need a second commit to fix it: git commit --amend replaces the last commit.

Fix the message

git commit --amend -m "Add the login page"

Without -m, git opens the old message in the edit pane, so you can change it, or save it as it is.

Add what you forgot

--amend builds its commit from the index, like any commit. So stage the missing file first, then amend:

git add login.css
git commit --amend -m "Add the login page"

Taking a file out works the same way. Stage its removal with git rm --cached <file>, which keeps the file on your disk, then amend.

Amend makes a new commit

A commit can never change. Amend makes a new commit with the same parent as the old one, and moves your branch to it. Watch the Live Graph: the new commit has a new id, and the old one turns faded, because no branch points at it any more.

The old commit isn't deleted straight away. git remembers where each branch has been, and main@{1} means "where main was one move ago". Rescuing lost work shows how to use that.

Only amend what you haven't shared

Amend only ever replaces the last commit on your branch. And because it swaps that commit for a new one, only amend commits you haven't pushed yet. Anyone who already has the old commit would end up with a history that no longer matches yours. Undoing in public shows the safe way to undo a commit others already have.