Sudoku Online
Play unlimited free Sudoku puzzles in four difficulty levels. Use notes, hints and undo, and race the timer. Your game is saved automatically.
How to use the Sudoku Online
- Choose a difficulty and press New game.
- Select a cell by clicking it (or with the arrow keys), then pick a number from the pad or type 1–9.
- Use notes to jot down possible numbers: turn on Notes (or press N) and tap numbers. Hold Shift while typing a number to add a note without switching mode.
- Stuck? Press Hint to reveal the selected cell, or Check to see any wrong numbers. Undo takes back your last move.
- Fill every row, column and 3×3 box with 1 to 9 to win. Your best time for each level is saved.
Sudoku tips for beginners
- Scan for singles. Pick a number and look at each 3×3 box. If there is only one cell in the box where that number can go, place it.
- Look for the last empty cell in a row, column or box. Whatever number is missing goes there.
- Use notes. Write the possible numbers in each cell. When a cell has only one note left, that's the answer.
- Find pairs. If two cells in a row, column or box can only hold the same two numbers, those numbers can be removed from every other cell in that group.
- Don't guess. Every puzzle here has one solution that can be reached by logic. If you're stuck, take a hint rather than guessing.
Keyboard controls
| Key | Action |
|---|---|
| Arrow keys | Move around the board |
| 1 – 9 | Enter a number (or a note when Notes is on) |
| Shift + 1 – 9 | Add or remove a note |
| Backspace / Delete | Erase the cell |
| N | Notes on or off |
| H | Hint |
| P | Pause or resume |
| Ctrl + Z | Undo |
Frequently asked questions
What are the rules of Sudoku?
Fill the 9×9 grid so that every row, every column and every 3×3 box contains each number from 1 to 9 exactly once. Some numbers are given at the start, and you can't change those.
Does every puzzle have a unique solution?
Yes. Each puzzle is generated and checked by a solver so that there's exactly one correct solution, which you can always reach by logic.
What is the difference between the difficulty levels?
Harder puzzles start with fewer given numbers: about 40 in Easy, 32 in Medium, 27 in Hard and about 24 in Expert. Fewer clues usually need more advanced solving techniques.
How do notes (pencil marks) work?
With Notes on, the numbers you enter are added as small candidates in the cell instead of an answer. When you place an answer, matching notes in the same row, column and box are removed automatically.
Will I lose my game if I close the page?
No. Your current game, notes and time are saved in your browser and come back when you return.
Can I play with a keyboard?
Yes. Use the arrow keys to move, 1–9 to enter, Shift+1–9 for notes, Backspace to erase, N for notes mode, H for a hint, P to pause and Ctrl+Z to undo.