Nurikabe: play the islands puzzle online

What is nurikabe?

Nurikabe is a shading puzzle on a square grid. Some cells hold numbers. Your job is to decide which cells are land and which are sea. Every number is the size of its island, so a 4 sits in a group of four land cells and a 1 is an island by itself. Everything that is not island is sea, and the sea has two rules of its own: it must be one connected body of water, and it may never form a 2×2 block.

That is the whole game, and it is enough to make a puzzle that you solve entirely by logic. You never need to guess. Each shaded cell follows from the numbers and the cells you have already settled.

You will also see it called the islands puzzle or the island and sea puzzle. The Japanese publisher Nikoli made it popular, and the name comes from a wall spirit in Japanese folklore.

Why the sea rules matter

The numbers tell you how big each island is, but not which way it grows. The two sea rules do most of the work. Because the sea must stay in one piece, an island can never wall off a patch of water. Because the sea cannot form a 2×2 block, every wide open area must hide some land. Most of the clever moves in nurikabe come from playing those two rules against the island sizes.

How to play nurikabe online here

Tap a cell once to shade it as sea. Tap it again to put a dot in it, which marks land that has no number. A third tap clears it. To shade a row of cells, press on the first one and drag across the others: every cell you pass gets the same mark as the first. On a keyboard, use the arrow keys to move, Space to cycle a cell and Backspace to clear it.

The tools under the board:

• Undo steps back one tap or one drag. Clear wipes the board, and Undo brings it back.
• Check outlines anything that breaks a rule (a 2×2 pool, an island with two numbers or too many cells, an island closed off before it is big enough, or sea cut off from the rest) and any mark that differs from the solution. Each wrong mark it finds counts as a mistake.
• Hint shades or dots one cell that follows from what is already on the board and tells you why in a short sentence. If one of your marks is wrong, the hint fixes that first.

Marks are never refused while you play. If you shade the right number of sea cells and the board is still not solved, the cells that break a rule are outlined in red so you can find the problem.

Pick Easy (7×7), Medium (10×10) or Hard (12×12) on the start card, or the Daily puzzle. Every board is built and checked by a solver before you see it, so there is always exactly one answer.

A simple way to solve nurikabe

1. Shade every cell beside a 1.
2. Shade every empty cell that touches two different numbered islands.
3. Count outward from each number and shade the cells no island can reach.
4. Look for islands with only one way out. If a 3 has a single empty neighbour, that cell is land.
5. Look for sea with only one way out. A shaded cell walled in on three sides must connect through the fourth.
6. Check every 2×2 square. Three shaded cells mean the fourth is land.
7. When an island is complete, shade all the cells around it, then go back to step 2.

Easy, medium and hard

Easy boards are 7×7 with islands of up to five cells, and you can finish them with the steps above alone. Medium boards are 10×10 with islands of up to seven cells, and at some point you will need to test a cell in your head: if this were sea, would the island next to it still have room to grow? Hard boards are 12×12 with islands of up to nine cells and more of those small what-if steps. The daily puzzle is a medium board.

Nurikabe and similar puzzles

If you like shading puzzles, Hitori asks you to shade repeated numbers while the white cells stay connected, and Akari has you place lights in a black and white grid. Fillomino is also about regions sized by their numbers, only you draw every region yourself. For number logic with regions, try Suguru.

How to play Nurikabe

1. Each number belongs to an island, and the island has exactly as many cells as the number. Every island holds one number, no more and no less.
2. Islands never touch each other side by side. Touching at a corner is fine.
3. All the shaded cells (the sea) join up into one connected area.
4. The sea never forms a 2×2 block of shaded cells.
5. Every puzzle has exactly one solution. Marks are never refused while you play: press Check to see rule breaks and wrong marks outlined in red, and each wrong mark it finds counts as a mistake.

Nurikabe tips

Surround the 1s straight away

A 1 is a complete island on its own, so all four cells beside it are sea. Shade them first. The same goes for any island that already has all its cells: everything around it is sea.

A cell between two numbers is sea

If an empty cell touches two different islands, making it land would join them into one island with two numbers. So it must be sea. Look for these cells wherever two numbers sit two steps apart in a row or column, or diagonally next to each other.

Never leave a 2×2 pool

When three cells of a 2×2 square are already sea, the fourth must be land. That land cell then has to belong to some island, which often tells you which way a nearby island grows.

Cells no island can reach are sea

Count outward from each number. An island of 3 can only reach two cells away from its number. Any cell that no island can reach with the cells it has left is sea, which settles big empty areas early.

Frequently asked questions