FREE GAME
Sudoku
Classic Sudoku with three difficulty levels, notes mode, and a mistake checker. Every puzzle has a guaranteed unique solution.
Why Use Our Sudoku?
Guaranteed Unique Solutions
Every puzzle is verified after generation to have exactly one solution, just like a properly published Sudoku puzzle.
Three Difficulty Levels
Choose Easy, Medium, or Hard based on how many starting clues are removed from the grid.
Pencil-Mark Notes Mode
Toggle Notes mode to jot down candidate numbers in any cell, exactly like writing small numbers in the corner of a paper puzzle.
Mistake Highlighting
Turn on Show Mistakes to instantly see any filled cell that doesn't match the solution, so you catch errors early.
Keyboard and On-Screen Input
Select a cell and type a number on your keyboard, or use the on-screen number pad - both work the same way.
100% Private
Every puzzle is generated and solved entirely in your browser. Nothing is ever sent to a server.
Frequently Asked Questions
Does every puzzle definitely have a solution?
Yes. Each puzzle is checked after generation to confirm it has exactly one solution, so there's never any guesswork beyond logic.
What does Notes mode do?
It lets you write small candidate numbers in a cell instead of a final answer, just like pencil marks on a paper puzzle.
How does the mistake checker work?
When Show Mistakes is on, any filled-in number that doesn't match the puzzle's solution turns red immediately.
Is this tool free?
Yes. It's free to use with no sign-up.
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