Sudoku is the number-placement puzzle with a single rule: each row, each column and each 3×3 box must contain the digits 1 to 9 exactly once. Every puzzle here is generated with exactly one solution.
Sudoku is a placement puzzle built on a 9×9 grid, divided into nine 3×3 boxes. Some squares are pre-filled; the rest you fill yourself. The only rule is also the whole game: every row, every column and every box must contain each of the digits 1 to 9 exactly once.
A well-made sudoku has exactly one solution — and crucially, it can be reached by logic alone. That is a design decision, not a coincidence: puzzles are generated by filling a grid and then removing digits one at a time, keeping a digit only if the puzzle still has a single solution after it has been taken away. Every puzzle on this site is built that way.
Beginners try to hold candidates in their head. Better players write them down. Pencil marks turn an invisible search into a visible one: as soon as a candidate disappears from every square in a row, the digit that remains in a square has to go there. Most of the puzzles rated easy and medium fall to that one technique plus patience.
The clock here is for your own curiosity. Nothing ends if you take an hour, and there is no limit on mistakes — a wrong digit is simply counted and can be corrected whenever you spot it.
Sites we publish ourselves — not paid placements.
opens in a new tabSee all our sites →