How to play
Nurikabe
Many islands.
One sea.
A number claims a little white island. Each sure move leaves the black sea a way through.
Its edge-neighbours must be black.
Reading view keeps each proof and its explanation together, without motion.
One means one. Including itself.
White squares make islands. Each island needs exactly one number, and that number is its total area. Squares in an island join through edges.
The 1 on the top row is already complete. Watch its three edge-neighbours turn black: adding any of them would make this island too big.
Does the 1 count its own square?
Choose an answer to check the reason.
Read the answer
Yes. The numbered square is part of its island. A 1 is complete immediately; its edge-neighbours must be black.
Black = sea. White = land. A dot means unknown, not white.
Give every number its own island.
Finish the borders around the other two 1s. Those black squares keep each tiny island at its exact size.
Now look between the two 2s, at row 4, column 3. It touches both numbers along an edge. What would happen if that square were white?
Between the two 2s: white or black?
Choose an answer to check the reason.
Read the answer
Black. Row 4, column 3 touches both numbered 2s by an edge. White there would put two clues in one island.
Dashed shapes are trials. Only a settled white or black square is a fact.
Leave a way through.
Black between the 2s keeps them separate. But the sea has a rule of its own: every black square must eventually connect through edges to every other black square.
Follow each isolated black square. Board edges and white clues block all but one exit. That exit must be black, or the square could never reach the rest of the sea.
Separate black patches are fine while unknown squares can still connect them. Corner contact alone does not connect them.
Three black squares. One white answer.
The outlined 2 × 2 block has three black squares. Making the fourth black would create a forbidden pool, so it must be white.
That new square joins the middle 2 and completes its island. The unknown square above the 2 must now be sea. The new white square also meets the right-hand 1 at a corner.
Incorrect black trial: it would make an all-black 2 × 2.
The middle 2 and right-hand 1 meet at a corner. Is that allowed?
Choose an answer to check the reason.
Read the answer
Yes. Corner contact is allowed. The white square at row 3, column 4 and the 1 at row 4, column 5 share a corner, not an edge.
A 2 × 2 black block is forbidden anywhere, even inside a larger black region.
One square keeps the whole sea together.
Trace the black group at the lower right. White islands surround it, and its only open exit is row 4, column 2. There is already black sea outside this group.
Try closing that exit with white. Every route out disappears. So the square must be black: it joins the group to the sea above and the black square on the left.
Incorrect white trial: it blocks the lower sea group’s only exit. Red outlines show the white blockers.
The amber lines show reachability through black squares. They are proof marks, not extra game pieces or a loop rule.
Use the sea to find the next shore.
Return to the top-left 2. A second 2 × 2 block now has three black squares. Its unknown corner must be white.
That white square joins the clue and gives the island exactly two squares. Earlier deductions have made this one visible.
Incorrect black trial: it would make an all-black 2 × 2.
Each island may bend. Its number fixes its area, not its shape.
One last island. One way to grow.
The bottom 2 still needs one white square. Above and right are black; below is outside the board. Only the square to its left remains.
Grow left to complete the island. Its final unknown edge-neighbour must then be black. Every square now has a reason.
No guessing, and no answer hidden behind the chart: each move followed a visible constraint.
Many islands. One sea.
Count the white islands: three single squares and three pairs. Each has one clue, each has the right area, and no islands share an edge.
Follow the branching amber trace through every black square. One sea, with no all-black 2 × 2 anywhere. That is a complete Nurikabe.
Every 2 × 2 window must contain white.
The trace can branch. Nurikabe asks for a connected sea, not a single unbranching path.
Chart your own seaA fresh chart.
Your way through.
A different 5 × 5, with only the clues given. Start with a 1. Later, the island of 4 will bend: islands need not be rectangles.
Practice stays in this page’s memory. Reload starts fresh. Regular games and saves are separate.
6 of 25 squares assigned · 0 marked sea groups
Start with a 1. Its edge-neighbours must be sea.
Clear your marks and begin a new attempt? You can undo the reset.
How to mark a square
Choose Sea, Land or Erase, then tap a square. Tap the same mark again to clear it. Numbered squares are fixed white land. Dots mean unknown.
Keyboard: Tab into the board. Arrow keys move. L marks land, S marks sea, Delete or Backspace erases. Enter or Space uses the selected tool. Tab leaves the board.
Mistakes stay until you erase or undo them. No conflict detected yet does not promise that a partial board can finish. Explain a move checks the current board; a useful preview records assistance immediately. Apply is a separate choice.
There is no timer. All 25 squares must be assigned and every rule satisfied to finish.
A little space
to think.
Count each island. Keep them separate. Leave the sea a way through. Your chart will grow here as you practise.
Play Nurikabe Return to your practiceFree to play. No account needed.
The quick rules.
- Every square finishes as white land or black sea. A dotted square is still unknown.
- White islands connect through edges. Each has exactly one clue and exactly that many squares, including the clue square.
- Different islands cannot share an edge. Corner touching is allowed. Islands may bend; they do not need to be rectangles.
- All black squares must form one edge-connected sea. Diagonal touching does not connect it.
- No 2 × 2 block may be entirely black, anywhere on the board.
A few good questions.
Does the number count itself?
Yes. A 1 is a complete one-square island. A 2 needs one additional edge-connected white square.
Must the sea make a loop?
No. It can branch and have dead ends. It only needs to be one edge-connected component, without any all-black 2 × 2 block.
Can black patches be separate while I solve?
Yes, while unknown passages can still connect them. Do not close every route out of a black patch if there is sea elsewhere.
Are all white groups already islands?
A partial white group may still need to grow to its clue. At completion every white group must contain exactly one number, with the right total area.
What do the amber lines mean?
They trace a reason through neighbouring squares. They are teaching overlays, not marks you need to draw in the regular game.