Nurikabe Solver, Step by Step
Type each number into its square. Walls show dark, island squares with a dot.
How to use the nurikabe solver
Set the width and height, then type each number into its square. Press Explain the next step: the solver shades the walls and marks the island squares that are certain, outlines what changed, and says why. Show the answer fills the grid at once and checks the solution is the only one.
The rules of nurikabe
Shade some squares as wall. Every number must end up in an island of white squares exactly that size, and each island has exactly one number. All the wall squares join up into one connected wall, and there is never a 2 by 2 block of wall anywhere.
How to solve nurikabe, step by step
Ones and neighbours. A 1 is an island on its own, so the squares beside it are wall, and a square touching two different numbers' islands must be wall, or it would join them. Count what each island can reach. Squares no island can get to with the squares it has left are wall. Close finished islands. When an island has its number of squares, wall it in. Watch the 2 by 2s. Three walls in a block make the fourth an island. Keep the wall joined. A piece of wall with only one way out has to take it, and so does an unfinished island. When those run out, the solver tries a square both ways and keeps the one that works.
How it was checked
The solver was run on all 110 puzzles of the daily nurikabe. It found each stored answer and found it to be the only one, and every step it explained was checked against those answers: it never shaded or cleared a square wrongly. 100 of the 110 were explained from start to finish; the rest need a longer chain of trial than it attempts, and it says so.
More logic puzzles
There is a new daily nurikabe every day. The nonogram solver and the slitherlink solver explain their steps the same way. For a puzzle you hold in your hands, see our brain teasers. There are more solvers on the puzzle tools page.
Frequently Asked Questions
How do you solve nurikabe?
Wall in every 1 straight away, and any square touching two different numbers. Shade squares no island can reach. Close each island once it has its number of squares, never leave a 2 by 2 block of wall, and keep the wall joined up: a piece of wall with only one way out has to take it.
What are the rules of nurikabe?
Shade squares as wall so that every number sits in an island of exactly that many white squares, each island has one number, all the walls connect, and no 2 by 2 block is all wall.
Can two numbers be in the same island?
No. Every island has exactly one number, which is its size, so a square that would join two numbered islands must be wall.
Why can't there be a 2 by 2 block of wall?
It is the rule that keeps the wall thin and forces the islands into place; without it many puzzles would have more than one solution.
Does every nurikabe have one solution?
A well-made one does. The solver checks, and says if the numbers you entered allow more than one.