How to play Sudoku

Play Sudoku

Sudoku has one rule, and no arithmetic at all. The digits are just nine different symbols — you could play it with letters or colours and nothing would change.

The rule

The grid has 81 cells, arranged as nine rows, nine columns and nine 3×3 boxes (the ones outlined in heavier lines). Fill every empty cell so that each row, each column and each box contains the digits 1 to 9 exactly once.

Some cells are filled in from the start. Those are the givens, shown shaded, and they can't be changed. Every puzzle on this site has exactly one way to finish it, and you can always get there by reasoning — you never have to guess.

Sudoku's original name is Number Place, from the American puzzle magazines where it first appeared in 1979.

An easy puzzle with 36 givens. The other 45 cells are yours. From Easy puzzle #1 — play it

The same puzzle, finished. Pick any row, column or box: each one holds 1 to 9 with nothing repeated.

Your first number

Beginners often stare at a single empty cell and try to work out what goes in it. That works sometimes, but there's an easier way in: pick a digit and ask where it can go.

Look at box 1, the tinted area. It still needs a 2. Each circled 2 rules out every empty cell it shares a row, column or box with, and once you've followed them all, only one cell is left — the one outlined in red. That's where the 2 goes. From Easy puzzle #1 — play it

That move is called a hidden single, and it's how most easy puzzles are solved from start to finish. Sweep the board one digit at a time, box by box, and you'll find them faster than you expect. When a sweep turns up nothing, the next trick is to look at a single cell and see which digits its row, column and box have already used up. If eight are gone, the ninth is the answer.

Those two ideas are enough for every Easy puzzle here. Medium and Hard ask for more, and the strategy guide walks through each technique with an example from a real puzzle.

Playing on this site

Tap a cell, then a digit on the pad. Tap the same digit again to clear it.
Notes switches the pad to pencil marks, the small candidate digits you jot in a corner while you think. When you place a digit, it's removed from the notes in that cell's row, column and box for you.
If a digit repeats in a row, column or box, both copies are marked straight away. A digit can be wrong without repeating anything, though, and that's what Check is for: it shows any cell that doesn't match the solution, but only when you ask.
Hint doesn't fill a cell. It tells you which technique to use next and where to look. The first hint on each puzzle is free; after that there's a one-minute wait between hints.
Undo and Redo go back as far as you like, and the game saves after every move.

Keyboard

Arrow keys move; 1–9 place a digit; Shift + digit writes a note.
N toggles notes, Z undoes, Y redoes, H asks for a hint.

Today's puzzle, then as many as you like

The first puzzle you get each day is the day's puzzle, the same for everyone, in Easy, Medium or Hard. Once it's done, Next puzzle gives you another, and another after that. Each one has a number, so you can send a friend the exact puzzle you just finished.

The daily puzzles follow the week. Monday's is the gentlest of its tier, they build through to Friday, Saturday has the week's toughest, and Sunday the second toughest — a little something for a slow morning.