Up to 100. Undo steps back through your numbers and notes one change at a time, and it works only within the puzzle you are playing.
You can undo up to 100 steps. Each number you enter, erase or add as a note counts as one step.
What undo covers
- Numbers you placed or erased.
- Notes you added or removed, including notes the game cleared automatically when you placed a number.
Undo steps back one change at a time, newest first. It cannot change the puzzle, and the given numbers were never part of your history.
Using it well
Undo is the safe way to test a line. If a number creates a conflict, step back instead of fixing things by hand. If you suspect a number earlier on was wrong, see whether you have to guess.
Your puzzle and its undo history are saved in this browser. For techniques that avoid needing it, read the Sudoku solving techniques guide or the full rules.