How to play Sudoku

The only rule

Fill the 9×9 grid so that every row, every column, and every 3×3 box contains the numbers 1 to 9 — each exactly once. Some cells come filled in; you work out the rest so nothing repeats in any row, column, or box. There's no adding up and no arithmetic — the numbers are just nine different symbols. It's pure logic.

How to start your first puzzle

Don't hunt for the emptiest corner — hunt for the most constrained one. Pick a row, column, or box that's already nearly full and ask which number is missing and where it can legally go. Often there's exactly one spot. That's called a single, and stringing singles together will carry you through any easy puzzle.

To play, tap an empty cell and then tap a number to drop it in. Tap the same number again, or use Erase, to remove it. The board highlights the digit you've selected across the grid and flags conflicts in red the instant two of the same number share a row, column, or box — so mistakes surface early.

What pencil notes are for

Once puzzles get harder, singles run out and you can't hold every possibility in your head. That's what notes are for. Switch on Notes and tap the digits that could fit a cell; they show up small, like pencil marks in a puzzle book. As you fill neighbouring cells, you cross candidates off until one answer is left standing. Notes are optional on easy, essential on medium and hard.

Do you ever have to guess?

No. A proper Sudoku always has exactly one solution, reachable by logic alone — and every puzzle on this site is checked to guarantee it. If you feel stuck, you haven't hit a dead end; you've missed a cell where only one number can legally fit. Slow down, re-scan the boxes, and it's there.

Ready to try it? Start with an easy puzzle, then work up to medium and hard as scanning turns into technique.