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Sudoku
Four levels, a daily puzzle and no guessing
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Fill the grid so every row, every column and every 3 by 3 box has the numbers 1 to 9 exactly once. Pick a square, then tap a number. Your game saves itself, so you can close the page and come back later.
How this sudoku works
Every puzzle here has exactly one solution, and you can reach it with logic. Our generator checks each one twice: once with a solver that counts solutions, and once with a solver that only uses moves a person would make. If a puzzle needs guessing, it never reaches you.
The levels mean something specific:
| Level | Numbers given at the start | What it takes |
|---|---|---|
| Easy | 36 to 40 | Spot the one number a square can hold |
| Medium | 27 to 34 | Also find the one square a number can use (hidden singles) |
| Hard | 24 to 31 | Pointing pairs and naked or hidden pairs |
| Expert | 24 to 32 | X-wings or naked triples |
Ranges measured on 200 puzzles per level from our own generator (120 for expert), October 2026.
Controls
- Notes: switch it on to pencil in small candidate numbers. They clear themselves when you place a number in the same row, column or box.
- Hint: fills in the square you picked, or the easiest open one, and says why. Up to 6 per puzzle.
- Undo goes back one move at a time, as far as you want.
- Keyboard: arrow keys to move, 1 to 9 to fill, Backspace to clear, N for notes, H for a hint.
- Mistakes: a wrong number turns red and you lose one of three lives. Three mistakes and the puzzle starts over. Notes never count.
- Settings lets you turn off the three-mistake limit, hide the timer, or turn off red mistake marks if you'd rather find errors yourself.
Questions
Is it really free?
Yes. No account, no download and no limit on puzzles. The site may show ads in the future to pay for itself; they'll never cover the board.
Will I lose my game if I close the page?
No. Your puzzle, notes and time are saved in this browser after every move. Clearing your browser data or switching devices starts fresh.
What's the fewest numbers a sudoku can start with?
Seventeen. In 2012, Gary McGuire, Bastian Tugemann and Gilles Civario ran an exhaustive computer search and showed no 16-clue sudoku has a single solution (paper: "There is no 16-Clue Sudoku", arXiv 1201.0749). Our puzzles start with 24 or more, which keeps them fair.
Can I print a puzzle?
Yes. The Print button prints the current puzzle's starting grid. For full sheets with answer keys, use printable sudoku.
More sudoku
- Daily sudokuA new easy, medium and hard puzzle every day, the same for everyone.
- Easy sudokuPlenty of clues. Every move can be found by looking for single options.
- Medium sudokuFewer clues, same simple logic. A good daily level.
- Hard sudokuNeeds pairs and pointing pairs, not just singles.
- Expert sudokuNeeds X-wings or triples. Still no guessing.
- Printable sudokuLarge-print sheets for pencil and paper, with answers.
- How to play sudokuThe rules, a first walk-through and the controls on this site.
- Sudoku strategiesFrom hidden singles to X-wings, with examples.