Nurikabe

Mark every square as land or sea. Each connected land island contains exactly one number and exactly that many squares, including its numbered square. Islands cannot join across an edge; they may touch diagonally. All sea squares form one connected area across edges. No 2 × 2 block may be entirely sea.

Choose Land, Sea or Erase, then tap a square. Tap the same mark again to clear it. Numbered squares are fixed land. A dot confirms land, waves mark sea, and grey blank squares are unknown. Ordinary mistakes remain until you change or undo them.

Keyboard: Tab to the board, then use arrows or Home/End to move. Enter or Space uses the selected action. L marks land; S marks sea; Delete or Backspace erases. Ctrl/Cmd+Z undoes; Ctrl/Cmd+Shift+Z or Ctrl/Cmd+Y redoes.

This finite collection has 12 original puzzles each at 5 × 5 and 7 × 7. Size is not a difficulty rating. Next stays at your size; restarting or switching size confirms before replacing unfinished choices.

Local saving resumes this browser's current board without an account or sync. Undo and redo history is session-only. When saving fails, keep this page open to retain progress.

A size-one island needs sea on each edge. Once an island reaches its number, surround its edge with sea. Three sea squares in a 2 × 2 block force the remaining square to be land. Keep room for the sea to connect.

Hint checks your current land and sea choices. It explains a supported local rule or a forced square proved by exhaustive island-shape search. Search is bounded: reaching its limit is uncertainty, not a contradiction. A contradiction means a choice needs changing or undoing.

Apply hint places the highlighted mark separately. Hints and reveals mark the puzzle as assisted. Reveal replaces the board only after confirmation.

Rules reference: Nikoli's Nurikabe rules. The code, explanations, diagrams and puzzles here are original.