GridPawHow to Play Nurikabe (Islands and Sea)
Nurikabe ("islands and sea") is a classic Nikoli logic puzzle. Some cells carry a number clue: each number is the exact size of an island — a connected group of white cells holding exactly that one number. All other cells are sea (dark), and the solver must obey three rules:
- Islands — each island is a connected group containing exactly one number, and its size equals that number. Islands never touch each other edge-to-edge.
- The sea — all sea cells form one single connected mass (an island may never cut the sea in two).
- No 2×2 sea — four sea cells in a square are forbidden.
GridPaw Nurikabe is the cat version: skinnier boards than the other GridPaw games (5×5 → 7×7 → 9×9), 4 heart-based tutorials, an 11-level campaign, then endless date-seeded daily puzzles — free, no sign-up. Play at gridpaw.com/nurikabe/.
Your First Puzzle
- Open the game. A How to play card pops up once (first visit) with a mini finished board and the 3 rules; tap "Got it — start with Tutorial 1". You're then on Tutorial 1/4 — a 2×2 board for rule 1. (Reopen anytime with 📖 How to play.)
- Cycle cells like traffic lights. Tap any non-number cell to cycle it: blank → sea ≈ → island → blank. Tapping the wrong value auto-corrects the cell to its true value, locks it for the level, and costs a heart — mistakes are warned, never left floating. Clue cells (with the little paw/plant icon and number) are fixed and can never be changed.
- Satisfy all three rules. The puzzle checks itself the moment every cell is known: wrong-but-complete boards get the message "Every cell is marked, but the islands don't match the numbers — some sea cells are actually island, or an island has the wrong size. Review and fix!"
Every Button on the Screen
| Control | What it does |
|---|---|
| Level chip (amber; green on tutorials) | Shows your position: Tutorial 1/4 — <lesson> · Level 4/11 — Medium — 7×7 · Daily — Medium 7×7 |
| ❤️ hearts chip | Your health: 3 hearts (❤️❤️❤️), lost hearts turn 🖤. Tutorials show ❤ ∞ (unlimited). |
| ↺ Restart | Discards the current board and generates a fresh puzzle at the same level |
| Skip tutorial » (only during the 4 tutorials) | Skips straight to campaign Level 1 — your first Easy 5×5 |
💡 Hint (badge shows 3) | Reveals exactly one correct cell — prefers an island cell — and tells you: "💡 Row 3, col 2 is sea ≈ — tap it once. (2 hints left)". 3 hints per level, refills on every new level. (Dev builds show ∞.) |
| 📖 How to play | Reopens the rules card with the mini-board diagram and tap instructions |
| Practice Medium 7×7 | Jumps to the first Medium board: Level 4/11 |
| Practice Hard 9×9 | Jumps to the first Hard board: Level 8/11 |
On Medium (7×7) and Hard (9×9), generating a board can take a couple of seconds, so a spinner overlay ("Generating puzzle…") covers the board while a Web Worker builds it off the main thread.
Difficulty Levels
| Stage | Grid | Notes |
|---|---|---|
| Tutorial ×4 | 2×2 → 3×3 → 4×4 → 5×5 | Seeded boards, one rule each: Islands and sea · The sea stays connected · No 2×2 sea · Corner pinning; auto-advances ~0.9s after each win |
| Easy ×3 | 5×5 | Pure constraint-propagation solvable |
| Medium ×4 | 7×7 | Pure constraint-propagation solvable |
| Hard ×4 | 9×9 | May need light backtracking |
| Endless Daily | 7×7 / 9×9 | Alternates medium/hard; date-seeded — same board for every player on the same day; after the campaign's 15 boards |
Campaign order is fixed: 3 Easy → 4 Medium → 4 Hard (Level N/11). Finishing the 11th unlocks "Campaign complete! Endless daily puzzles unlocked."
Winning, Losing & Sharing
Winning. When every cell is correct, the victory popup shows Solved! (or Daily solved!), a pixel-grid reveal where all island cells flip to amber in a ≤1s cascade, and Next level → (tutorials auto-advance instead). The win overlay carries the 3 share buttons:
- 📋 Copy — copies the share text (✅ Copied, 1.5s): "🌊 Sank GridPaw Nurikabe Level N — every island in place, sea stays one. Don't drown → gridpaw.com/nurikabe/" (daily variant: "no hearts lost")
- 𝕏 Share — opens the board card first (rendered image of your solved board, tagged "GridPaw Nurikabe · Level N", footer gridpaw.com/nurikabe/)
- 👽 Reddit — same board card, posts to r/gridpaw
In the board card: 📋 Copy Image, ⬇️ Save (gridpaw-nurikabe-levelN.png), 𝕏 Post, 👽 Post, ✕ Close.
Losing. Wrong marks cost a heart per mistake (not in tutorials — they only count mistakes). Losing all 3 hearts opens the 💔 Out of hearts overlay: "Three wrong marks — this board got away from you. A fresh one is coming up." Tap New board ↻ for a fresh puzzle at the same level. Campaign progress is saved automatically (gridpaw-nurikabe-progress) and resumes next visit.
Frequently Asked Questions
Do I need an account to play Nurikabe?
No — playable fully logged out, no account system in-game.
My tap did nothing on a number cell. Why?
Correct: clue cells are fixed islands — they can't be changed.
It auto-corrected my cell and locked it. What happened?
That's the tutorial-style guard: wrong marks are corrected to the truth, locked for the level, and cost a heart. Use it as free information.
I'm stuck. What do I do?
💡 Hint reveals one correct cell (3 per level). And watch the tell-tale pattern from Rule 3: three ≈ cells around one corner force the fourth cell to be island.
What is the Daily puzzle?
After the campaign, every level is date-seeded: same board for everyone that day, alternating Medium (7×7) / Hard (9×9), refreshed daily.
Medium/Hard takes a moment to load?
Normal — the board is generated in a Web Worker and shown behind a spinner.
Is this the same as classic Nurikabe?
Yes — identical rules (islands match numbers, connected sea, no 2×2 sea). GridPaw adds cat styling and unlimited generated boards.
Why does the game mention "≈"?
≈ is the sea marker on marked sea cells.
Are Hard boards solvable without guessing?
The generator validates every board has exactly one solution before serving it (solveNurikabe count = 1).