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Fill the 9×9 grid so that every row, column, and 3×3 box contains the digits 1–9 exactly once. Tap an empty cell to select it, then tap a number from the panel to fill it in. Use pencil mode to jot down candidate numbers without committing to an answer.

One Sudoku offers four levels: Easy, Medium, Hard, and Expert. Easy puzzles have more given numbers and are great for beginners. Expert puzzles require advanced techniques and are suited for experienced solvers.

Tap the pencil icon in the toolbar to toggle notes mode. In notes mode, tapping a number adds it as a small candidate note inside the cell without committing it as a final answer. Toggle back to normal mode to enter final answers.

Tap the undo button (↩) in the toolbar to step back one move at a time. You can undo as many times as you like.

A fresh puzzle is available every day — the same puzzle for every player worldwide. Completing it extends your daily streak. Miss a day and your streak resets.

No. One Sudoku is fully playable as a guest — every difficulty, the Daily Challenge, and all your stats work without signing in. An account is optional and only exists so your progress can follow you to another device.

Open Settings (gear icon) inside the app and choose Sign In. You can use Sign in with Google, Sign in with Apple, or an email address and password. Once signed in, your progress syncs automatically.

If you are signed in, your progress, stats, and streaks are synced to your account and restored automatically when you sign in on another device or reinstall the app. As a guest, your game data stays on your device — it is included in iCloud Backup (iOS) or Google Backup (Android) if you have those enabled in your device settings.

Go to Settings → Account → Delete Account inside the app. This permanently removes your account and all progress synced to our servers. If you cannot sign in, email us and we will handle it — full instructions are on our Delete Account page.

One Sudoku is only available in English.

Go to Settings (gear icon) inside the app and tap "Reset All Progress". This clears all statistics, streaks, and completed puzzles. If you are signed in, it also clears the copy synced to your account. This action cannot be undone.

Yes. Puzzles are generated on-device, so you can play anywhere without an internet connection.

Yes, One Sudoku shows small banner ads at the bottom of the screen to keep the app free. You may also see a short ad after completing a puzzle. Additionally, you can choose to watch a video ad to earn extra hints — this is entirely optional.

One Sudoku is available on the App Store for iPhone and iPad, and on Google Play for Android phones and tablets.