Make room for discovery.

Install on your home screen

On iPhone or iPad, open this website in Safari, use Share, then Add to Home Screen. On Android or desktop, use your browser’s Install app or Add to Home Screen option where available. On Mac Safari, choose File → Add to Dock. Open the site in its own browser tab if an embedded preview does not show installation options. Installation is optional: you can also play in your browser.

Play offline

Keep the app open online until “100 puzzles and the local generator are ready offline” appears under App & storage. The included puzzles, hints, explanations, and custom puzzle generation will then work without a connection. A first visit still needs the internet. Custom puzzles are constructed and their deductions checked locally in a background worker. Complex rule blends may take longer; use Cancel to stop without losing previous progress.

Keep your discoveries

Progress saves automatically in this browser. Use “Protect saved progress” to ask the browser to retain site storage, and download a backup before clearing browser data or changing devices. A browser can deny that request, and private browsing may discard data when it closes. Backups include pencil marks, colors, history, and saved custom puzzles.

Restoring a backup replaces this app’s saved plays in the current browser. It does not merge two histories. The backup is checked before restoration. Keep a copy of your current progress if you want to return to it.

Play and learn

Drag to select several cells. Use Center marks, Corner marks, or Colors to annotate them. Tap a rule chip to explain that rule. Hints reveal an idea gradually, with optional questions for cages, thermometers, and arrows. A practice answer never changes the grid or counts as a mistake.

Get help

Email sudoku@area9.dk. Include your device and browser, what happened, and a puzzle link if relevant. A screenshot can help; avoid sending a progress backup unless you intend to share its history.

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