A little help, if you need it.

Room to learn.

The basics

Fill each row, column, and 3×3 box with the numbers 1 through 9, once each. Tap a cell, then a number. Starting clues cannot be changed. Undo restores your entries and notes; Erase clears the selected editable cell.

Challenge or Classic?

Challenge checks each entry against the unique solution immediately. A wrong entry stays out of the board and adds a strike, even when it doesn't repeat a nearby number. Three strikes end the attempt by default; change the limit for new games in Settings. Undo does not remove strikes. You can retry or continue in Classic.

Classic lets you explore without automatic correctness feedback or strikes. Choose Check Board from the game menu when you want a check. A full, valid board completes automatically.

Pencil notes

Tap Notes to switch the keypad to small candidate numbers. Tap a candidate again to remove it. Notes are manual by default. Settings lets you enable a Fill Notes menu action and optional automatic cleanup. These use the numbers currently on the board, not the hidden answer. Note changes are undoable.

Your kind of puzzle

Choose Easy, Medium, Hard, or Expert from the rated collection, or opt into puzzles generated on your device. Every puzzle has one unique solution. Custom controls the number of empty squares; it isn't a difficulty rating. If a sparse custom request cannot be generated, try again or choose fewer empty squares.

Make it yours

Fresh installs start on Medium in Challenge mode. A saved game always resumes unchanged. New Puzzle remembers your last successfully started difficulty, mode, source, and custom count on this device; changing your mind and cancelling never replaces your game.

Settings offers Ink, Moss, and Clay themes, plus System, Light, Dark, or Scheduled appearance. Scheduled switches at your chosen local times. The timer is hidden by default, and all gameplay works offline.

Save it like an app

iPhone / iPad: Open GridZero Play in Safari, tap Share, choose Add to Home Screen, and confirm Add (enable Open as Web App if offered). It opens in its own app-like window.

Android: Open GridZero Play in Chrome or another browser with installation support. Choose Install app or Add to Home screen from the browser menu. Wording varies by browser.

No app-store account or purchase is needed for the web app. Visit once online over HTTPS and let the game load before going offline. Browser storage is local, not a backup or sync service; clearing site data, storage eviction, or private browsing may remove saves or caches. An installed web app may have a separate storage container from your browser tab, depending on your OS.

Found something?

Play in your browser with the same rules and puzzle collection. Use arrow keys to select a cell, 1–9 to enter, N for notes, Backspace to erase, and Control/Command+Z to undo (Shift to redo). The game works offline after its first successful load on HTTPS. Your browser save is separate from your native app save. Haptics are available only on browsers that support vibration.

Open a GitHub issue with your device model, OS version, and what happened. A screenshot helps. Please keep private information out of public issues.