Shape the islands. Connect the sea. Discover what must be true.
Numbered cells are permanent island cells. Islands may touch the board edge. The sea does not need to make a border. A completed board has no unknown cells and satisfies every rule.
Choose Mark Island, Mark Sea, or Erase, then tap or click a cell. The active tool is visibly selected. Unknown cells have a dot, unnumbered island cells have a circle, and sea cells have a wave. These symbols can be switched off in settings.
Right-click with a mouse to mark sea. Optional Drag painting paints one state throughout a stroke and groups that stroke as one undo action. Press Escape to cancel a stroke. Turning drag painting off restores ordinary touch scrolling and pinch navigation; a scrolling gesture does not mark cells.
| Key | Action |
|---|---|
| Arrow keys | Move the cell focus |
| Home / End | Move to the start / end of a row |
| I | Select Island and mark the focused cell |
| S | Select Sea and mark the focused cell |
| E / Delete / Backspace | Select Erase and clear the focused cell |
| Enter / Space | Use the selected marking tool |
| Ctrl / ⌘ Z | Undo |
| Ctrl / ⌘ Shift Z | Redo |
| Escape | Cancel a stroke or close a dialog |
Focused cells announce their row, column, clue if present, and state to screen readers. Tab moves out of the grid to the other controls.
A little hint first highlights a relevant area and names the deduction. Explain why gives the reasoning and proposed marking. Apply marking makes that one change. A usable hint counts as assistance as soon as it is shown, even if you choose not to apply it.
Hints analyze your current markings. They check that at least one legal completion remains before suggesting a cell. Simple rule explanations are used when available. A deeper solver-assisted hint is explicitly labeled; it proves a marking by exhaustively trying its opposite. No stored solution lookup is described as a logical deduction. Analysis has a time limit; if no marking is proved in that time, no cell is guessed.
Check board outlines direct rule violations and also checks whether a legal completion remains. It does not mark solution cells. Two sea regions are allowed on a partial board when unknown cells could connect them. Automatic direct error feedback is optional and off by default.
Browse 100 verified, uniquely solvable puzzles: 20 each in Beginner, Easy, Medium, Hard, and Expert. Filter by difficulty, dimensions, or status. Every puzzle keeps a separate saved board and up to 150 undo and redo positions. Opening the game resumes your most recent puzzle.
Difficulty is an algorithmic estimate, not a guarantee of how a person will experience a puzzle. Beginner puzzles use basic deductions and at most a small amount of reach reasoning. Easy puzzles are solved by a combination of those rules and reach deductions. Medium puzzles need island-shape reasoning but no branching in the verifier. Hard puzzles require some verifier search; Expert puzzles require deeper or broader search. Board-size limits keep introductory puzzles compact. The collection includes boards from 5 × 5 to 15 × 15.
Today’s puzzle selects one of these verified puzzles using your device's local calendar date. Everyone using this same collection and date gets the same selection. A daily selection may repeat on different dates.
The optional timer stops while the puzzle is paused, complete, hidden in a background tab, or a game dialog is open. Hide it without affecting play. Restart clears the current attempt and its move history after confirmation; previous completion records remain.
Revealing the solution requires confirmation and records that attempt as revealed. Undoing a reveal does not remove that designation. Restart to begin a fresh attempt. Progress statistics keep your best category for each puzzle: independent takes precedence over hinted, then revealed. A later independent solve can upgrade an earlier assisted record. These categories are mutually exclusive in the statistics.
Choose a marking tool, then tap. Zoom controls stay below the board. Fit keeps smaller puzzles comfortable; large grids preserve usable cell sizes and scroll within their own frame. Zoom in for larger targets. Focus and cell coordinates stay with the same grid cell when zoom changes. Drag painting is optional and disables normal navigation within the board while enabled.
High contrast, cell symbols, automatic rule feedback, timer visibility, and helpful status messages are under Make yourself comfortable. Reduced-motion settings on your device are respected.
Progress stays in this browser on this device. No accounts or uploads are used. Clearing browser data, changing browsers or website addresses, and some private-browsing settings can affect saved progress. If storage is blocked or full, the game stays playable and displays a message. If saved data is malformed or an unsupported version, the original data is kept untouched and new writes are disabled for that session.