Kurodoko (Kuromasu)

Shade cells so each number equals the white cells it can see in its row and column, itself included.

Kurodoko is a logic puzzle on a grid where some cells hold numbers, and this free tool lets you play it right in your browser. You shade cells so that each number matches the count of open cells it can see, with no account or sign-up needed. Kuromasu is another name for the same puzzle.

You can choose a 7×7, 9×9 or 11×11 grid and an Easy, Medium or Hard level. Each puzzle is generated on your device from a random seed. The board checks your marks against the rules, and a hint explains the next logical step when you get stuck. The page works on phones, tablets and computers. Your progress saves automatically in your browser, so you can close the tab and come back later without losing your place. Puzzles you print here are free to use in class or in products you sell, such as KDP books or Etsy printables.

How to use the Kurodoko tool

Pick a size: 7×7, 9×9 or 11×11. The default is 9×9.
Pick a Difficulty: Easy, Medium or Hard. Then press New puzzle. “Generating…” shows while the new puzzle is made.
Click or tap a cell to shade it. Click or tap it again to clear it. Numbered cells cannot be shaded.
Right-click, or use the Dot chip, to mark a cell that should stay unshaded.
Press Hint when you are stuck. It highlights the cells involved and explains in one sentence which rule proves the next step. If you have made a wrong mark, it points at that mark first.
Press Check to see cells that break a rule or differ from the solution, shown in red. If nothing is wrong, it says “No mistakes so far” with the percentage done.
Undo and Redo step back and forward; Restart clears the board but keeps the puzzle.
When the page says “Solved in m:ss”, press Next puzzle. If you want the answer, press Show solution.

With a keyboard, move with the arrow keys, shade with Space, mark a dot with X or ., and clear a cell with Backspace. On a phone or tablet, the Shade and Dot chips above the board choose what a tap does, and the Move chip lets you scroll a zoomed board. Print prints the puzzle; tick “Print the answer page too” to add the solution. Press Copy link to share the exact same puzzle or continue on another device.

Kurodoko rules

Kurodoko is a grid puzzle where some cells hold numbers, and you shade cells to meet three rules. Each number equals the count of unshaded cells it can see in its row and column, counting its own cell and stopping at a shaded cell or the edge of the grid.

Numbered cells are never shaded.
Shaded cells never touch along a side.
All unshaded cells form one connected area.

A number is always at least 2, because a cell that saw only itself would be cut off from the rest of the unshaded area.

How to solve kuromasu

Solving kuromasu means using logic, one small step at a time. The tool’s solver names its techniques, and for a number k they work like this:

Easy puzzles are solved with four techniques:

Adjacent: the neighbours of a shaded cell stay unshaded.
Full: if all the cells a number could possibly see add up to exactly k − 1, they are all unshaded.
Stop: if the cells it already surely sees add up to k − 1, the next cell in each direction is shaded.
Escape: an unshaded group with only one way to link up with the rest must go that way.

Medium puzzles also need two more:

Reach: if the other three directions together can give at most m cells, this direction must give at least k − 1 − m.
Cut: a cell whose shading would split the unshaded area stays unshaded.

Hard puzzles need trial and error. You assume a cell is shaded, follow the consequences, and if a rule breaks, you know the cell must stay unshaded.

For an example, the first hint on the 9×9 Easy puzzle with seed 3 says the 2 at row 1, column 6 already sees 2 cells through cells known to be unshaded. Nothing more may be seen, so row 3, column 6 is shaded.

Is kurodoko the same as kuromasu

Yes. Kurodoko and Kuromasu are two names for the same Nikoli puzzle, so the rules and techniques above apply to both. This page uses the name Kurodoko.

Frequently asked questions

Is kurodoko free, and do I need an account?

Yes, it is free. There is no account or sign-up, progress and settings are saved in your browser, and nothing is uploaded.

Can I play kurodoko on a phone?

Yes. It works on phones, tablets and computers. Fit, the default, sizes the board to the screen width, and Zoom in and Zoom out change the size if you need it.

Can I print a kurodoko puzzle?

Yes. Press Print to get the puzzle on its own page with its size, difficulty and rules. Tick “Print the answer page too” to add the solution on a second page, and choose Save as PDF in the print dialog if you want a file. A4 and Letter both work.

Does every kurodoko puzzle have one solution?

Yes. Each puzzle is generated from a random seed and kept only when the site’s own solver proves it has exactly one solution, so it can always be finished by logic.

Why does the puzzle title show a different level from the one I picked?

If a size cannot produce the level you asked for, the closest level is used. The puzzle title shows the real level, so you always know what you are playing.

Can I use kurodoko puzzles from here on Etsy or in a book?

Yes. Kurodoko puzzles from this page are royalty-free for personal, classroom and commercial use, including KDP books, Etsy printables, Teachers Pay Teachers and print-on-demand. No credit is required. The only thing you may not do is copy the generator or the site itself to run a competing service; see the terms.

Hitori: Use it when you want a shading puzzle where you remove duplicate numbers from a grid.
Nurikabe: Use it when you want to build walls around numbered islands on a grid.
Light Up (Akari): Use it when you want to place lamps so every open cell is lit.
Heyawake: Use it when you want a region-based shading puzzle with room-count clues.
Tapa puzzle: Use it when you want to shade cells based on clues describing their neighbours.
Star Battle: Use it when you want to place stars so each row, column and region has the same number.
Nonogram: Use it when you want to fill a grid using row and column number clues.
All puzzles on the site: Use it when you want to see every puzzle type available here.

Updated October 2026