Play Kurodoko Online Free

Kurodoko first appeared in Nikoli issue 34 in June 1991. Its clues count visible white cells in four orthogonal directions, including the clue cell itself, until a black cell or the grid edge blocks sight. You must also keep black cells from sharing an edge and preserve one connected white area. These linked rules exercise counting, connectivity planning, and contradiction checking. Read one large visibility clue, mark the cells it must see, and begin solving Kurodoko online.

1. Treat every numbered cell as white. Its number counts itself plus consecutive white cells seen up, down, left, and right. Diagonal cells never contribute, and the count stops at the first black cell in each direction.
2. Compare a clue with the maximum cells it could currently see. If its number equals that maximum, mark every visible candidate white. If the clue already sees enough confirmed white cells, place black blockers at the next possible cells where required.
3. Whenever you shade a cell black, mark its four orthogonal neighbors white because black cells cannot touch by an edge. Then update all clues whose sight lines pass through the new blocker.
4. Protect white connectivity as the grid fills. If shading a candidate would split the remaining white cells into separate components, mark that candidate white. Narrow white corridors often force this decision.
5. Finish when every clue sees exactly its number, no two black cells share an edge, and all white cells connect through orthogonal steps. Verify each sight line from the clue outward rather than counting an entire row or column.

• Numbered cells always remain white. Count the clue cell once, then add visible consecutive white cells in the four cardinal directions.
• A black cell blocks visibility. Cells beyond it do not count for that clue, even when they are white and lie in the same row or column.
• Black cells may touch diagonally but cannot share a horizontal or vertical edge. Every orthogonal neighbor of a black cell must therefore be white.
• All white cells must form one orthogonally connected area. Corner contact alone does not connect two white groups.
• Unnumbered cells may become black or white. The final assignment must satisfy every visibility clue, black-cell separation, and white connectivity simultaneously.

• Calculate each clue's directional budget. Subtract one for the clue itself, then distribute the remainder among up, down, left, and right. Grid edges and known blockers cap each direction and can force minimum extensions elsewhere.
• Use the plus-one blocker rule. When a clue has exactly n visible white cells along a completed combination of arms, the next cell beyond each established arm must be black where it exists, or the clue would see too far.
• Exploit adjacent clues. Two clues in one line often share a visible segment. Compare their totals and edge distances to determine whether a blocker must sit between them or beyond one clue.
• Audit articulation cells before shading. A cell that forms the only white route between upper and lower areas cannot become black. Mark it white, then reconsider any clue that can see through it.
• Chain black separation with visibility. A forced black cell creates white neighbors; those white cells may lengthen a clue's sight line to its target, which then forces another blocker. Follow the chain until no new state appears.

• Yajilin: Yajilin also forbids edge-adjacent black cells, but arrow clues count black cells and the remaining cells carry a loop. Kurodoko uses white visibility and white-area connectivity instead.
• Aquarium: Aquarium fills cells under gravity and checks line totals. Kurodoko shades blockers to control sight lines. Both ask players to connect local cell states with rules that reach across a row or column.

• Three rule systems support one another. A blocker settles sight lines, its neighbors become white, and those white cells may preserve the only route through the grid.
• Visibility clues stay concrete. Players can recount a plus-shaped field at any moment and identify exactly where an extra or missing white cell occurs.
• Connectivity adds forward planning. A locally legal black cell may still fail globally, giving experienced solvers a second layer of deductions beyond simple clue arithmetic.

Play Kurodoko online for free with cell shading, white marks, and clue numbers displayed clearly. The browser lets you reverse a tentative state and recount affected sight lines without erasing paper. Start with large clues near edges, follow each forced black cell into its white neighbors, and watch the remaining white network. Difficulty options support a short introduction or a longer connectivity challenge.

Kurodoko has challenged Nikoli readers since issue 34 in June 1991. Count from each clue along its four arms, stop at black blockers, separate every black pair, and keep the white cells connected. Strong solves combine these requirements rather than treating them in isolation. Begin above with a clue at its maximum reach, mark its visible cells white, and follow the resulting blockers and corridors until one connected white area remains.

• Kurodoko rules (Nikoli)