How to play
A Sudoku board is a 9×9 grid, divided into nine 3×3 boxes. Some cells already contain digits. Those given digits do not change. You fill every empty cell so that each row, each column, and each box contains the digits 1 through 9 exactly once.
The same digit may appear many times on the board. It may not appear twice in the same row, the same column, or the same box. A finished board is complete only when all three of those checks pass. More detail and a labeled diagram are in the rules guide.
Placing a digit
Select an empty cell, then select a digit. If you turn on Select Number First in Settings, you can hold a digit and tap several cells to fill them in a row. Erase clears the digit or the notes in the selected cell. Given digits cannot be erased.
Notes, Undo, and Hint
- Notes switches to pencil marks. A note is a candidate, not a final answer. See how notes work.
- Undo steps back through your recent moves.
- Hint fills one cell when you are stuck. The rest of the board is still yours to solve.
Settings that change a game
- Auto-Clear Notes removes a digit from notes in the same row, column, and box when you place that digit.
- Hide Completed Numbers hides a digit on the keypad after it has been placed in all nine of its cells.
- Limit Mistakes to Three ends the puzzle after three incorrect entries. With the limit off, a wrong digit is still wrong, but the puzzle does not end.
Killer and Daily Challenge
Killer adds cages. Digits in a cage must be unique and must add up to the small number shown on the cage. The ordinary row, column, and box rules still apply. Cage sums walks through a small example.
Daily Challenge starts from the home screen. If you leave, Continue Last Game reopens that board in the same browser. Continuing a game explains what is saved and what is not.