Sudoku
Nine boxes. One solution. Choose your challenge.
How to play and strategy · Best scores stay in this browser when storage is available.
Sudoku: how to play and strategy
Nine boxes. One solution. Choose your challenge.
How to play
Choose a difficulty, then select a square and use the number pad or keys 1–9. Arrows move between squares. N toggles pencil notes; Delete or Backspace erases; Ctrl/Cmd + Z undoes.
Rules and progression
Fill the 9 × 9 grid so every row, column and each of the nine 3 × 3 boxes contains 1–9 exactly once. Starting numbers are fixed: Easy gives 45, Medium 36, Hard 30 and Expert 26. Every puzzle has one solution.
Red squares show repeated numbers. Notes help track possibilities, and Undo restores your previous entry. Complete puzzles for a difficulty bonus; each difficulty keeps its own best score.
Worked example: turn candidates into a forced move
If a row contains 1, 2, 3, 4, 5, 6, 8, and 9, its empty square must be 7. If it instead has two empty squares and lacks 3 and 7, check their columns and 3 × 3 boxes. A square whose column already contains 3 cannot be 3. That fixes it as 7 and leaves 3 for the other square.
Plan your next move
- Check row, column, and box before writing notes. Each unit can eliminate a candidate.
- After placing a number, revisit the units crossing that square. One placement can expose another forced move.
- A number can avoid a red duplicate warning and still be wrong. Look for a reason that forces it, not just the absence of a warning.
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