Sudoku
Select a square to begin.
How to play
Fill every row, column, and three-by-three box with the digits 1 through 9, using each digit exactly once per group. Click a square and type a digit, or use the keypad. Arrow keys move around the board, and Backspace clears a square.
Every puzzle has exactly one solution, and your progress is saved in this browser automatically.
Board options
Open Options beside the keypad to set the board up the way you like it. You can highlight the row, column, and box of the square you have selected, pick out every square holding the same number as that square — both in any colour and strength — and have digits that do not belong turn red as you place them. All three are off-by-choice: turn them off for a plainer puzzle.
Possible numbers prints the candidates for each empty square in a small three-by-three grid. Set it to Auto to have every digit that still fits worked out for you, or Manual to pencil them in yourself — switch the keypad to Notes and tap the digits you want to keep track of.
Hint selects the square that is easiest to work out next and explains why it is solvable, without filling it in for you. If something on the board already contradicts the solution, it points you there first.