How to play Sudoku
Fill every row, column, and 3×3 box with the digits 1 through 9. Each digit may appear only once in each unit.
Start with what is forced
Choose an empty cell and inspect its row, column, and box. Cross out digits already present. When only one candidate remains, place it. You can also scan a unit for a digit that has only one possible position.
Turn on Notes or press N, then add the small digits that may fit a cell. Correct placements automatically remove that digit from peer notes.
Use Hint, then Explain why
Press H or select Hint to highlight a target without revealing the answer. Select Explain why to see the strategy, candidates, and reason. The board changes only after Apply step or Shift + H at the explanation stage. When no supported logical single is available, Sudoku0 labels the option as a solution-backed reveal.
Controls
- Use the number pad or keyboard digits 1–9 to enter a value.
- Use arrow keys to move one cell, and Home or End to move within the current row.
- Use Delete or Backspace to erase, N to toggle Notes, and Escape to pause.
- Use Ctrl/Cmd + Z to undo and Shift + Ctrl/Cmd + Z to redo.