How to play Sudoku
Sudoku is played on a 9×9 grid made of nine 3×3 boxes. The single rule: every row, column and box must contain the digits 1–9 exactly once. There is no arithmetic. Only logic. A well-formed puzzle, like every puzzle on this page, has exactly one solution that can be reached by deduction alone.
The four difficulty levels
- Easy: 40+ given clues. Solvable with simple row/column/box scanning.
- Medium: 33–39 clues. Adds basic elimination and hidden singles.
- Hard: 28–32 clues. Requires naked pairs and pointing pairs.
- Expert: 23–27 clues. Needs advanced patterns such as X-Wing, Swordfish and XY-chains.
Does Sudoku really help the brain?
Research links regular number-puzzle solving with maintained cognitive performance. A 2019 study in the International Journal of Geriatric Psychiatry (n≈19,000) found adults over 50 who regularly played number puzzles had brain-function scores equivalent to people ten years younger. Sudoku is also widely used in classrooms and care settings as a screen-friendly logic exercise.
How the puzzles are generated
Every puzzle on this site is made fresh on request. There is no stored bank of fixed boards. A backtracking algorithm fills a blank 9×9 grid, then removes clues one at a time. After each removal, the solver runs again to confirm exactly one valid solution still exists. The number of clues left standing at the end sets the difficulty. Reload the page and a new, fully verified board appears.