Sudoku
Fill every row, column and 3×3 box with the digits 1-9. Every puzzle has exactly one solution.
About this Sudoku
Every row, every column, and every 3×3 box must contain the digits 1 through 9 with no repeats. Tap a square, then tap a number below the board (or use your keyboard) to fill it in; given squares are shown in a shaded background and can't be changed.
Every puzzle is generated with a guaranteed unique solution, verified before it's ever shown — the same standard used across the puzzle-generation tools on this site. A full grid is built first, then squares are removed one at a time, checking after each removal that exactly one solution still exists; a removal that would create a second valid solution is undone and a different square is tried instead.
If a number you place conflicts with another in its row, column, or box, both squares are highlighted so you can spot the mistake immediately rather than discovering it later. Your best time is saved separately for each difficulty.
Frequently asked questions
Can a Sudoku puzzle ever have more than one valid solution?
Not here — every puzzle is checked by a solver before it's shown, confirming exactly one valid completion exists. If removing a square would allow a second solution, that square is kept and a different one is tried instead.
What does the highlighting mean when I make a mistake?
Any squares that share a row, column, or box and contain the same number are highlighted, so a conflict is visible immediately rather than only showing up once the board is full.
How is difficulty decided?
By how many squares are given at the start — Easy leaves the most clues, Expert the fewest. Every difficulty still gets the same uniqueness guarantee.
Can I use a physical keyboard?
Yes — select a square, then press 1-9 to fill it or Backspace/Delete to erase it.