Mouse
- Left click: toggle sea/island color
- Right click: toggle note/unknown (if supported)
- Drag: paint multiple cells (if supported)
Overview 
Nurikabe
누리카베
Grow numbered islands and paint the rest as one connected sea—without 2×2 pools.
A clean binary puzzle where one wrong cell can break an island or create an illegal pool.
Logic PuzzleBinary Puzzle
Goal & Core Rules
Color the grid to form islands matching the numbers, while the remaining cells form one connected sea with no 2×2 blocks.
- Each number is an island cell; the number equals the size of that island (orthogonal connectivity).
- Each island contains exactly one numbered cell.
- All sea (black) cells must be connected as one region.
- No 2×2 block of sea cells is allowed.
Controls
Keyboard
- Arrow keys: move cursor (if supported)
- B/W: set sea/island (if supported)
- U: set unknown (if supported)
Touch
- Tap: toggle state
- Long-press: alternate color/note (if supported)
- Drag: paint multiple cells (if supported)
Beginner Tips
- Mark obvious sea: cells that can’t belong to any island due to distance limits.
- Watch for forced separation—two islands cannot touch orthogonally.
- Use the no-2×2 rule early; it creates many quick deductions.
Advanced Tips
- Prevent sea disconnection: avoid painting cells that would isolate a sea pocket.
- For each numbered island, track its maximum expansion area to eliminate impossible cells.
- When a narrow corridor appears, decide early whether it must be sea to keep connectivity.
Origins & History
Nurikabe is a logic puzzle named after the “invisible wall” yokai in Japanese folklore. It was developed and popularized through Nikoli’s Puzzle Communication magazine, with an early publication credited to “renin” in 1991.
Timeline
- 1991 An early Nurikabe puzzle was published in Puzzle Communication Nikoli (issue #33) and the genre quickly gained popularity.
Notable People
- Nikoli Publisher that developed and popularized the puzzle
- renin (れーにん) Credited with early publication in Nikoli magazine
Sources
FAQ
Can islands touch each other?
No. Different islands cannot connect orthogonally—otherwise they would merge.
Why is 2×2 sea forbidden?
It prevents ambiguous “pools” and helps keep the puzzle logically constrained.
What should I do first?
Use the biggest numbers and the no-2×2 rule to lock down early forced cells.