How to play Sudoku

Sudoku is the world's most popular pencil puzzle, and it needs no arithmetic at all — just patient logic. The board is a 9×9 grid divided into nine 3×3 boxes. A handful of digits are filled in for you; the rest is up to you to work out.

Goal

Fill every empty cell so that each row, each column, and each of the nine 3×3 boxes contains the digits 1 through 9 exactly once — no repeats anywhere. Every puzzle we generate has one and only one correct solution, and the given clues are always enough to reach it by reasoning alone. You never have to guess.

Controls

• Click a cell to select it, then click a number on the pad or press a key from 1 to 9 to place that digit.
• Turn on Notes to pencil-in small candidate numbers — the possibilities you're still weighing for a cell. A pencil mark clears automatically once that digit is placed in a cell that shares its row, column, or box.
• Erase empties the selected cell. Hint fills the selected cell with its correct digit when you're truly stuck.
• A digit that breaks a row, column, or box turns red so you can spot the mistake. The timer keeps running until every cell matches the solution.

Difficulty

Pick your level before you start. Easy hands you around 40 clues for a gentle warm-up; medium gives 32; hard drops to 26; and expert leaves just 22, demanding deeper chains of deduction. Whichever you choose, the puzzle is checked for a unique, no-guessing solution before it ever reaches the board.

Tips

• Scan for "naked singles" — cells where only one digit can possibly fit — and "hidden singles," where a digit can only go in one spot within a row, column, or box.
• Use Notes generously on harder grids. Seeing the candidates laid out turns a tangled puzzle into a series of small, obvious eliminations.
• When progress stalls, switch the cell you're staring at. A digit that's hard to place by row may be easy to place by box.