Frequently Asked Questions

Sudoku is a logic-based number puzzle. The goal is to fill a 9×9 grid with digits so that:

• Each row contains all numbers from 1 to 9
• Each column contains all numbers from 1 to 9
• Each 3×3 box contains all numbers from 1 to 9

Use logic and process of elimination to determine where each number should go!

No! 9sudoku.com is completely free to use without any registration. Just visit our website and start playing immediately.

We offer 5 difficulty levels:

• Simple: Perfect for beginners (46 clues)
• Average: Good for casual players (40 clues)
• Difficult: Challenging puzzles (33 clues)
• Master: For experienced players (29 clues)
• Expert: Ultimate challenge (22 clues)

The Notes feature helps you keep track of possible numbers for each cell:

• Click the "Notes: OFF" button to turn on Notes mode
• When Notes mode is on, clicking numbers will add small notation marks to the selected cell
• This helps you remember which numbers might fit in that position
• Click the Notes button again to return to normal input mode

The Hint feature provides you with the correct number for the selected cell. Select any empty cell and click "Hint" to reveal the answer for that position. Use hints sparingly to maintain the challenge!

Yes! Click the "Undo" button to reverse your last action. You can undo multiple moves in sequence to backtrack through your solving process.

The Timer tracks how long you've been working on the current puzzle, and the Counter shows how many moves you've made. Both can be toggled on or off using the "Timer: ON/OFF" and "Counter: ON/OFF" buttons.

Absolutely! 9sudoku.com is fully responsive and works great on smartphones, tablets, and desktop computers. The interface automatically adapts to your screen size for the best experience.

Yes! 9sudoku.com works as a Progressive Web App (PWA). Once you've visited the site, you can continue playing even without an internet connection.

9sudoku.com works on all modern browsers including Chrome, Firefox, Safari, and Edge. We recommend keeping your browser updated for the best experience.

Try these steps:

• Refresh the page (F5 or Ctrl+R)
• Clear your browser cache and cookies
• Disable browser extensions temporarily
• Try using a different browser
• Check your internet connection

If problems persist, please contact us!

All our puzzles are automatically generated and verified to have exactly one solution. If you think you've found an error, please double-check your work first. If you're still confident there's an issue, please contact us with details about the puzzle.