About This Tool
Play Sudoku puzzles in your browser with multiple difficulty levels. Fill the 9x9 grid so that every row, column, and 3x3 box contains the digits 1-9 exactly once. Features pencil marks, undo, hints, and auto-checking for errors.
How to Use
Select a difficulty level — Easy, Medium, Hard, or Expert.
Click an empty cell and type a number (1-9) or use the on-screen number pad.
Use pencil marks to note possible candidates for a cell.
If you get stuck, use the hint feature to reveal one cell.
Complete the entire grid correctly to solve the puzzle.
Frequently Asked Questions
How are difficulty levels determined?
Difficulty is based on how many cells are pre-filled and which solving techniques are required. Easy puzzles can be solved with basic logic, while Expert requires advanced strategies.
What are pencil marks?
Pencil marks are small candidate numbers you can add to a cell to track which values are still possible. They help with advanced solving techniques like naked pairs and hidden singles.
Can every puzzle be solved?
Yes. Every generated puzzle has exactly one solution, verified by the generation algorithm.