How to play Sudoku
The board is a 9×9 grid split into nine 3×3 boxes. Fill every empty square with a digit from 1 to 9 so that each row, each column and each 3×3 box contains every digit exactly once. The starting digits cannot be changed. Every puzzle here has exactly one solution and can be solved by logic, without guessing.
- Enter a digit: select a square, then tap a number on the pad or press 1–9.
- Notes: turn on Notes (or press N) to pencil in candidates. Shift+digit adds a note without switching modes. Placing a correct digit removes that digit from notes in the same row, column and box.
- Move: arrow keys. Erase: Delete or Backspace. Undo: Ctrl+Z. Pause: P.
- Mistakes: a digit that does not match the solution is shown in red and counted.
- Hint: fills the selected square with the correct digit, or the most constrained empty square if none is selected.
- Number pad: the small number under each digit shows how many of that digit are still to be placed.
- Saved game: the current puzzle, notes and timer are kept on this device. The timer pauses when you switch tabs.
Difficulty levels
- Easy: 36 or more starting digits. Solvable by finding squares with only one possible digit.
- Medium: about 30 starting digits. Still solvable with singles only, but they are harder to spot.
- Hard: needs candidate eliminations such as pointing pairs and naked or hidden pairs.
- Expert: needs techniques beyond pairs, such as X-Wing or chains of candidates.
Solving techniques
Naked single
A square where eight of the nine digits already appear in its row, column or box. Only one digit is left, so it goes there.
Hidden single
Within one row, column or box, a digit that can only go in one square — even if that square has other candidates.
Pointing pair
If all candidates for a digit inside a box lie in the same row, that digit can be removed from the rest of that row outside the box. The same works for columns.
Naked pair
Two squares in the same unit with the same two candidates, for example 4 and 7. Those two digits must go in those two squares, so remove 4 and 7 from every other square in the unit.
Hidden pair
Two digits that can only go in the same two squares of a unit. Every other candidate can be removed from those two squares.
X-Wing
A digit that, in two rows, can only go in the same two columns. It must occupy opposite corners of that rectangle, so it can be removed from the rest of both columns.
Frequently asked questions
Does every puzzle have one solution?
Yes. Each puzzle is checked for a single solution before it is shown.
Is there a limit on mistakes?
No. Mistakes are counted and shown with your result, and the game continues.
Are my best times saved?
Your best time for each level is stored on this device and shown when you solve a puzzle.