About Sudoku
Sudoku is the world's favorite number puzzle. Fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1 to 9 exactly once. Every puzzle here is generated fresh and checked to have exactly one solution.
Pencil in candidates with Notes, undo any move, and ask for a hint when you are stuck (it adds 20 seconds). Three mistakes end the puzzle. Choose Easy, Medium, Hard or Expert, and beat your fastest time on each.
How to play
- Select a cell, then tap a number or type 1-9.
- Turn on Notes (N) to write small candidate numbers.
- Each number can appear only once in its row, column and 3×3 box.
- Completed rows, columns and boxes light up green.
Sudoku rules
A Sudoku grid has 81 cells arranged in nine rows, nine columns and nine 3×3 boxes. Some numbers are given at the start. Fill every empty cell with a digit from 1 to 9 so that each row, each column and each box contains every digit exactly once. A well-made Sudoku has only one correct solution, and you never need to guess to find it.
Solving techniques, from easy to advanced
- Scanning. Pick a digit and look across the rows and columns that already contain it. Often only one cell in a box is left where that digit can go.
- Naked single. If a cell can hold only one digit, because the other eight already appear in its row, column or box, write it in.
- Hidden single. If a digit fits in only one cell of a row, column or box, it must go there, even if that cell has other candidates.
- Notes. On Hard and Expert, turn on Notes (key N) and pencil in the candidates. Patterns become much easier to see.
- Naked pairs. When two cells in the same unit can only hold the same two digits, those digits can be removed from every other cell in that unit.
- Pointing pairs. If a digit's candidates inside one box all sit in the same row or column, you can remove that digit from the rest of that row or column outside the box.
Which difficulty should you choose?
Easy starts with 40 given numbers and can be solved by scanning alone. Medium gives 33, and Hard gives 28, where notes and hidden singles become essential. Expert removes as many clues as the puzzle allows. For reference, mathematicians proved in 2012 that a classic Sudoku needs at least 17 clues to have a single solution.
Common Sudoku mistakes
- Guessing a number "to see what happens". One wrong digit can spoil the whole grid.
- Forgetting to update notes after placing a digit.
- Checking only rows and columns but not the 3×3 box.
Enjoy logic puzzles? Try Nonogram picture logic or the classic Minesweeper, or browse all puzzle games.
Sudoku FAQ
Do I need maths to play Sudoku?
No. The digits are just symbols; Sudoku is pure logic, with no adding or multiplying.
Is there a hint button?
Yes. Press H or the Hint button to reveal one correct cell, and Ctrl+Z to undo a move.
