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 Explain before Apply step
Press H or select Explain to preview the strategy, target, candidates, observation, and conclusion. The board does not change until you select Apply step or press Shift + H. When no supported logical single is available, Sudoku0 labels the suggestion as a solution-backed guided reveal rather than pretending it is a deduction.
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.