What Is Kuromasu? Rules, Shading, and Beginner Tactics

What is Kuromasu, exactly?

What is Kuromasu? Also written Kurodoko, Kuromasu is a shading puzzle built around a single elegant idea: each numbered cell tells you how many cells it can see. The grid starts with a scattering of numbered white cells, and your job is to shade some of the other cells black so that every number counts correctly. A numbered cell sees itself plus all the white cells stretching away in the four directions until a black cell or the grid edge stops the view. Kuromasu blends counting with careful shading logic, and it has a clean, almost architectural beauty once the black cells settle into place. For solvers who enjoy visibility puzzles and connected-region thinking, Kuromasu is a rewarding and slightly underrated gem.

The rules of Kuromasu

The rules of Kuromasu are few but powerful. Every numbered cell is white and stays white; its number equals the total count of white cells visible in the four orthogonal directions, including the numbered cell itself, stopping at the first black cell or the edge in each direction. You shade some of the unnumbered cells black to satisfy all of the numbers at once. Two black cells may never be orthogonally adjacent, so no two shaded cells share an edge. At the same time, all of the white cells must remain connected into one single group, so the black cells can never wall off a pocket of white. Balancing the exact visibility counts against these two structural rules is the whole art of solving a Kuromasu puzzle.

Here is a worked example. A cell numbered one can see only itself, which means all four of its orthogonal neighbors must be black; those blacks sit around the numbered cell without touching each other edge to edge, so the rule against adjacent blacks is respected. At the opposite extreme, a large number demands long clear runs of white cells reaching out in several directions, which tells you those lines cannot be interrupted by shading. When two numbered cells lie in the same row or column, the space between them is tightly constrained, because a black cell there would cap both of their views at once. Reading these counts carefully, while keeping the white region connected, lets you place black cells with confidence and no guesswork.

Beginner tactics for Kuromasu

• Start with the smallest numbers; a one forces all four neighbors black and a two nearly pins its surroundings as well.
• Treat each number as counting itself plus the unbroken white cells in all four directions, then test where a black must cap the view.
• Keep black cells apart, since two shaded cells can never share an edge, which often forces nearby cells white.
• Protect connectivity; reject any black cell that would seal off a group of white cells from the rest of the grid.
• Use pairs of numbers in the same line to fix the black cell that limits both of their sight distances.

How Kuromasu compares to Sudoku

Compared with Sudoku, Kuromasu trades symbol placement for visibility and shading, yet the underlying discipline is the same. Sudoku asks for each of nine symbols exactly once per row, column, and box through elimination, while Kuromasu asks you to shade cells so every number sees precisely the right count of white cells. Both puzzles guarantee one solution and reward steady, guess-free logic. If you enjoy the calm, orderly satisfaction of Kuromasu, you might also like Mystic Sort, a soothing sorting game from the studio behind Shapedoku. And when you want the classic every-symbol-once challenge with a warm, cosmic atmosphere, Shapedoku reimagines Sudoku with nine glowing shapes in place of numbers so you can solve by color and form. It is colorblind-friendly by design, with a free solver and printable puzzles at shapedoku.com and instant play at app.shapedoku.com.