What is Kuromasu?
Kuromasu is a Japanese logic puzzle, also known as Kurodoko, where you decide which empty cells are black and which cells stay white. The numbered cells are clues, and each clue tells you how many white cells it can see in its row and column.
Visibility travels up, down, left and right from the clue. It includes the clue cell itself, passes through other white clue cells, and stops when it reaches a black cell or the edge of the grid.
- Numbered cells must always stay white.
- Each number counts the visible white cells in four directions plus itself.
- Black cells cannot touch horizontally or vertically.
- All white cells must connect orthogonally in one area.
- The puzzles generated here are checked for a single solution before play begins.
How to play Kuromasu online
Click or tap an empty cell to shade it black. Click again to mark it as white, and use Erase when you want to clear a square. Clue cells cannot be shaded, because every numbered square is part of the white connected area.
Use Check for feedback without revealing the answer. Hint fills one useful square from the unique solution, while Solution shows the completed grid if you want to study the logic.
- Start with small numbers, because they usually need nearby black cells.
- Look at large numbers to find long visible white corridors.
- When you place a black cell, mark its orthogonal neighbours white.
- Keep checking that the white cells can still connect.
- Use the clue totals to decide where visibility must stop.
Kuromasu grid sizes and difficulty
The 6x6 Kuromasu board is a friendly place to learn the rules. The 8x8 board gives a balanced daily puzzle, and the 10x10 board creates longer sight lines where one black square can affect several clues at once.
Easy puzzles use more clues and more immediate deductions. Medium puzzles remove some of that scaffolding. Hard puzzles leave more open cells, so you have to combine visibility counts, black-cell spacing and white-cell connectivity.
- 6x6 Kuromasu is best for learning the rule set.
- 8x8 Kuromasu is a balanced everyday challenge.
- 10x10 Kuromasu gives the most room for advanced strategy.
- Easy, medium and hard change clue density and solving pressure.
- Every new puzzle is generated and checked for uniqueness.
Kuromasu strategy tips
A good Kuromasu strategy is to treat every number as a line-of-sight equation. If a clue already sees enough confirmed white cells, the next possible cell in each open direction must be black. If a clue needs every remaining visible cell, those cells must stay white.
The black-cell rule is just as powerful. Because black cells cannot touch orthogonally, every black cell immediately forces up to four neighbouring cells to be white, which can extend or complete clue sight lines.
- Count the minimum and maximum cells each clue can still see.
- Use black cells as blockers for clues that would otherwise see too far.
- Use white marks to protect the connected white area.
- Scan for places where two clues demand the same blocker.
- Before guessing, ask whether a black cell would isolate a white region.
Why unique Kuromasu puzzles matter
A fair Kuromasu puzzle should have one final shading pattern. If two different sets of black cells satisfy the same clues, the player has to guess which answer the puzzle intended.
This online Kuromasu game checks the clue set with a solver before it appears. That keeps Check, Hint and Solution aligned with the same single answer, and it makes the difficulty settings feel like real logic rather than random clue removal.