How do pencil marks work?

Toggle pencil mode (the 🖊️ button) and tap numbers to add/remove candidates in a cell. Pencil mode is a separate tap target so you can plan without committing. Auto-fill pencil marks fills every cell with all valid candidates given the current grid.

Are puzzles unique-solution?

Yes. The generator validates that each puzzle has exactly one solution, so logical play always reaches the right grid without guessing.

What's the difficulty range?

Four levels: Easy, Medium, Hard, and Expert. Difficulty is set by the number of givens and the techniques required to deduce the rest — Expert puzzles need X-wing-class reasoning, not just hidden singles.

Does it work on mobile?

Yes. The grid scales to the viewport and number entry uses an on-screen pad. Undo/redo, hint, and pause are all touch-friendly.

Can I import a puzzle?

Not yet — the New Game dialog generates puzzles in-browser. There's no paste-from-newspaper input today; the generator is the source of new puzzles.

Sudoku — Free Classic Number Puzzle 🔢

Time 0:00

Hints 0

Mistakes 0

⏸

Paused — tap to resume

Arrows to move • 1–9 to fill • N for notes • H for hint •