Sudoku Online

✓ Free Online Sudoku Puzzle, Multiple Difficulty Levels

Free browser-based Sudoku with unique-solution puzzles, four difficulties, notes and hints — everything runs and saves on your device.

🧩 Unique-Solution Puzzles — A backtracking generator builds fresh boards and verifies each has exactly one solution.
🎚️ Four Difficulties — Choose intro, easy, medium or hard — difficulty scales with how many cells are removed.
✏️ Pencil Notes — Toggle note mode to jot candidate numbers in a neat 3×3 mini-grid inside any cell.
🚦 Conflict Highlighting — Optional real-time checking flags duplicate numbers in any row, column or box in red.