About the game
Sudoku is a logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. Some cells are pre-filled with numbers. Your task is to fill every empty cell with a digit from 1 to 9 so that each row, each column, and each 3×3 box contains every digit exactly once.
Despite its name (Japanese for "single number"), Sudoku originated in Switzerland and was popularized in Japan in the 1980s. The beauty of Sudoku is that it requires zero arithmetic — only pure logic. Every puzzle has exactly one solution, and it can always be found through deduction alone.
How to play
- Look at the pre-filled numbers. Each row, column, and 3×3 box must contain 1-9 exactly once.
- Use logic to determine which numbers go in empty cells. Look for rows, columns, or boxes that are nearly full.
- Click a cell and enter a number. Use pencil marks (notes) to track possibilities.
- Fill the entire grid correctly to solve the puzzle.
Controls
| Select cell | Click or tap |
| Enter number | 1-9 keys or on-screen number pad |
| Pencil mark / note | Click the note icon or press N, then enter numbers |
| Erase | Backspace or click the erase button |
Five beginner tips
1. Start with "naked singles"
If a cell has only one possible number (all others are in its row, column, or box), fill it in immediately.
2. Scan by number
Focus on one number at a time (e.g., all the 5s). See where it can go in each row, column, and box.
3. Use pencil marks
Mark possible numbers in empty cells. As you fill in more numbers, the possibilities shrink and patterns emerge.
4. Look for hidden singles
If a number can only go in one cell within a row, column, or box — even if that cell has other candidates — it belongs there.
5. Don't guess
Sudoku is a logic puzzle. If you are guessing, you have missed a deduction. Go back and scan again.
Why you'll like it
Sudoku is the ultimate thinking game. No timer, no pressure — just you and the grid. The satisfaction of watching a tangle of numbers resolve into perfect order is uniquely rewarding.
Frequently asked questions
Are the puzzles solvable by logic alone?
Yes. Every puzzle has exactly one solution reachable through pure deduction.
Can I undo a move?
Yes — erase a cell and try again.
Are there different difficulty levels?
Yes — the puzzle generates easier or harder boards based on how many numbers are pre-filled and the deduction techniques required.
Game credit: Open-source Sudoku implementation. MIT licence.