The rules
A Sudoku is a 9x9 grid divided into nine 3x3 boxes. Some cells come filled in; these are the givens. Your job is to fill the rest so that every row, every column and every box contains each digit from 1 to 9 exactly once. That is all. No adding, no arithmetic of any kind. The digits could be nine letters or nine colours and the puzzle would play identically.
A properly made puzzle has exactly one solution, and you can reach it by reasoning alone. Every board on this site is checked for that before it is shown to you. So when you are stuck, the next move exists somewhere on the board; the techniques below are ways of finding it faster.
How a game works here
- Tap a cell, then tap a digit. Tap the same digit again to clear it.
- Notes lets you pencil small candidate digits into a cell. When you place a digit, it is removed from the notes of every cell in the same row, column and box.
- Relaxed mode highlights mistakes and lets you carry on. Challenge mode ends the game at three.
- Three hints per puzzle. A hint places one correct digit and costs a little score.
New to the game entirely? The beginner's guide walks through a first puzzle from the opening move to the last cell.