How to play Nurikabe
Shade a connected river around numbered islands — each island as big as its number. Also known as Islands in the Stream.
The rules
- Some cells hold numbers. Each number belongs to an island of exactly that many unshaded cells.
- Each island contains exactly one number.
- All shaded cells (the river) form one connected group.
- No 2×2 block may be entirely shaded.
- Islands may not touch each other side to side.
Playing Nurikabe on Puzzle Solvers
- Pick a grid size and difficulty and press New Puzzle.
- Click a cell to shade it; click again to clear it. Right-click or long-press to mark a cell you are sure stays unshaded.
- Undo, Hint and Check are on the toolbar; the Progress panel counts shaded cells and rule violations.
- Send to Solver shows the full solution step by step; Send to Slate puts the puzzle on a Slate whiteboard.
Using the Nurikabe solver
- Choose a grid size and enter the island numbers in their cells; leave every other cell blank (or press Sample).
- Press Solve: islands grow from their clues, the river is shaded, and each deduction is listed.
A worked example
A clue 1 sits in a corner. Its island is complete, so both neighbours are river.
A cell sits between a 2 and a 3 clue, touching both. If it were island it would connect two numbered islands, which is not allowed — so it is river.
Strategies
- Ones are complete. An island of size 1 is just its clue cell — shade all its neighbours.
- Between two clues. A cell touching two different numbered islands must be river, or it would join them.
- Unreachable cells. A cell too far from every clue to be part of any island must be river.
- Avoid 2×2 pools. If three cells of a 2×2 square are river, the fourth must be island.
- Keep the river flowing. A river segment with only one way out must extend through it.
Common mistakes
- Leaving a 2×2 block of river.
- Letting two islands touch because each has the right size.
Where it comes from
Nurikabe was popularised by a Japanese puzzle publisher in 1991. The name comes from a creature of Japanese folklore — an invisible wall that blocks travellers.
Frequently asked questions
Can islands touch diagonally?
Yes — only side-to-side contact is forbidden.
Why can't the river have a 2×2 block?
It is the rule that keeps the river narrow and the puzzle uniquely solvable.
How do I mark an island cell in the game?
Right-click or long-press a cell to mark it white (island). Click to shade it as river.
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