Daily Nurikabe
The rule
Flood the board, leaving an island at every number. Each number says how many squares its island has, and no island holds two numbers.
Islands never touch side to side. The water is all one piece, and it never contains a two by two block of itself.
Tap a square to flood it. Tap again to mark it as land you are sure of, and once more to clear it.
Where to start
A square touching two different numbers must be water: no island may hold two. That one fact opens most boards.
Then count. The land adds up to the sum of the numbers and nothing else, so the amount of water is known before you begin. A 1 is finished where it stands, so everything round it is water.
The no two by two rule does more work than it looks. Three corners of a square already flooded force the fourth to be land, wherever it is.
In your hands
Carving a shape out of what is left is what a packing puzzle asks in wood. More in 2D packing.
One Answer, Found by Search
Each board is made by growing the water first as a thin connected wall, which leaves islands behind it, and reading the numbers off those. Then the numbers get moved about inside their own islands: a number says how big its island is, not where it sits, so the choice is free, but it is not free in its effect. The same islands with the numbers somewhere else can go from several answers to exactly one. Boards that cannot be pinned down that way are thrown out, which is most of them.
A word on what is promised here, because it is not quite what the other grids on this site promise. Those are checked by a solver that only uses techniques a person can use, so they are guaranteed to need no guesswork. For nurikabe that check exists but is not strong enough to finish these boards, so what is guaranteed is narrower and plainly true: every board has exactly one answer, confirmed by exhaustive search. How much of it falls out of pure reasoning depends on how many techniques you know.
More to Play
There are twenty four daily sudoku variants, a hashiwokakero, a numberlink and a slitherlink.
If you like a puzzle that yields to patience rather than luck, that is exactly what a good interlocking puzzle asks of you. See the 6 Piece Cross, or the rest of the collection.
Frequently Asked Questions
How do you play Nurikabe?
Flood the board, leaving an island at every number. Each number says how many squares its island has, and no island holds two numbers.
Is Nurikabe free to play?
Yes. There is a new nurikabe here every day, free, with no account and nothing to install. It plays in the browser on a phone or a computer, and it remembers where you got to.
Can every puzzle be solved?
Every board has exactly one answer, confirmed by exhaustive search. Unlike the other grids here no promise is made that pure reasoning will get you all the way; how far it takes you depends on how many techniques you know.