Fill each row, column, and 3×3 box with the numbers 1–9. No number may repeat within the same row, column, or box. Use pencil marks to track candidates before committing to a value.
Controls
- Click / Tap – select a cell
- Keyboard 1–9 – place numbers
- Shift + number – toggle pencil marks
- Backspace / 0 – clear cell
- Ctrl+Z / Ctrl+Y – undo / redo
Strategies
- Single Candidate: when only one number fits a cell.
- Single Position: when a number can only go in one cell of a row, column, or box.
- Pencil Marks: quickly highlight potential digits to aid deductions.
- Notes & Hints: toggle auto-check or use hints for guidance.
Teacher Mode Tips
- Enable pencil marks and strict mode for classroom lessons.
- Use Mini 4×4 puzzles to introduce Sudoku logic to younger learners.
- Track weekday streaks to encourage consistent practice.