Nurikabe is a logic puzzle published by Nikoli. You are given a grid with some numbered cells. The goal is to shade (blacken) certain cells so that the shaded cells form one connected 'sea,' no 2×2 area is entirely shaded, and each numbered cell belongs to a white 'island' whose size matches its number.

How do you solve a Nurikabe puzzle?

Start by identifying cells that must be shaded or white. Cells between two different islands must be sea. A 1-island is just the numbered cell itself — shade all its neighbours. Expand larger islands step by step, shading cells that would create a 2×2 pool or disconnect the sea.

What grid sizes are available?

Three sizes: 7×7 (quick puzzles for beginners), 10×10 (a balanced challenge), and 14×14 (larger grids for experienced solvers wanting a longer session).

What difficulty levels are there?

Three levels: Easy (more numbered cells and simpler island shapes), Medium (fewer clues, requiring more deduction), and Hard (minimal clues demanding deep logical reasoning). All puzzles have a unique solution solvable with logic alone.

What is the 2×2 pool rule?

No 2×2 block of cells may all be shaded (sea). This 'no pool' constraint is a key rule that prevents trivially large sea areas and provides important deduction opportunities throughout the puzzle.

Play Nurikabe Online

Shade cells to build a connected sea. Each numbered cell anchors a white island of that size. No 2×2 pools allowed!

Sea

Time

0:00

Tap a cell to shade it (sea) — tap again to mark white (island)

What Is Nurikabe?

Nurikabe is a binary-determination logic puzzle first published by the Japanese puzzle company Nikoli in 1991. The name comes from Japanese folklore — a nurikabe is an invisible wall that blocks travellers at night. In the puzzle world, the “wall” is the connected sea of shaded cells you build around numbered islands.

The puzzle is played on a rectangular grid. Some cells contain a number. Your task is to determine which of the remaining cells are sea (shaded/black) and which are island (white). The result is a clean partition of the grid into exactly one contiguous sea and several separate islands, each anchored by its numbered clue.

Rules of Nurikabe

Islands match their number: Each numbered cell is part of a white island. The island is a connected group of white cells (orthogonally adjacent) whose total size equals the number shown.
One number per island: Each island contains exactly one numbered cell. No island may contain two or more numbers.
Connected sea: All shaded (sea) cells must form a single orthogonally connected group.
No 2×2 pools: No 2×2 block of cells may all be sea. This “no pool” rule prevents trivial solutions and provides crucial deduction points.
Unique solution: A well-formed Nurikabe puzzle has exactly one solution, reachable through pure logic with no guessing.

How to Solve Nurikabe Puzzles

1. Shade Between Different Islands

If two numbered cells are adjacent or separated by a single cell, the cells between them must be sea — otherwise their islands would merge, violating the “one number per island” rule. This is often the very first deduction you can make.

2. Expand Size-1 Islands

A cell showing 1 is a complete island by itself. All four of its orthogonal neighbours must therefore be sea. Mark them immediately.

3. Use the No-Pool Rule

After shading some cells, check every potential 2×2 block. If three of the four cells in a block are already sea, the fourth cannot be sea — it must be white (island). This rule triggers constantly and drives many deductions.

4. Ensure Sea Connectivity

If shading a cell would split the sea into two disconnected regions, that cell cannot be island. Conversely, if leaving a cell white would isolate a pocket of sea, it must be shaded to keep the sea connected.

5. Unreachable Cells Are Sea

A cell that cannot be reached by any island (because every nearby island is already at its required size, or the cell is too far from any number) must be sea. Count distances from each clue to identify these.

6. Island Expansion by Elimination

If an island still needs to grow (its current white region is smaller than its number) and can only expand in one direction, that direction is forced — those cells must be white.

Grid Sizes & Difficulty Levels

7×7 — Easy: Compact grid with generous clues. Great for learning the rules and basic techniques.
7×7 — Medium/Hard: Same grid size but fewer islands or islands of larger size, requiring longer deduction chains.
10×10: The classic Nurikabe experience. Balanced density with room for complex sea-connectivity reasoning.
14×14: Large grids for experienced solvers. Longer solve times and more intricate island/sea interactions.

Nurikabe vs Other Logic Puzzles

vs Nonograms: Both reveal a pattern of shaded cells, but Nonograms use row/column clues while Nurikabe uses island-size numbers placed in the grid.
vs Minesweeper: Both have numbered clues affecting neighbours, but Minesweeper hides information (mines) while Nurikabe is fully visible from the start.
vs Hitori: Both involve shading cells on a grid, but Hitori eliminates duplicate numbers in rows/columns while Nurikabe partitions the grid into islands and a connected sea.
vs Light Up (Akari): Both are Nikoli puzzles with constraint propagation, but Light Up places objects (bulbs) while Nurikabe classifies cells as sea or island.

Frequently Asked Questions

Nurikabe is a logic puzzle where you shade cells on a grid to form a single connected sea. Numbered cells define white islands — each island’s size must equal its number, and no 2×2 block can be entirely shaded.

Start by shading cells between different numbered clues. Expand size-1 islands by shading all their neighbours. Use the no-pool rule, ensure sea connectivity, and identify cells unreachable by any island.

Three sizes: 7×7 for quick games, 10×10 for the classic experience, and 14×14 for a bigger challenge.

Easy (many island clues, simpler shapes), Medium (fewer clues, more deduction), and Hard (minimal clues requiring deep reasoning). All puzzles have a unique solution.

No 2×2 block of cells may all be shaded (sea). This constraint is central to the puzzle — it prevents large featureless sea regions and provides frequent deduction opportunities.

More Puzzle & Strategy Games

If you enjoy Nurikabe, try these other free games on our site:

Light Up (Akari)

Place bulbs to illuminate every cell on the grid.

Hitori

Shade duplicate numbers so no row or column repeats.