Rules
Kurodoko is a shading puzzle. The board is a square grid. Thin lines divide the cells. A thick frame sits around the outside. A number counts every white cell it can see in a straight line up, down, left, and right, including itself. A shaded cell blocks the view. The number itself stays white. Shaded cells never share a side. They may touch at a corner. The white cells of the whole board share sides in one group. You shade a cell, or you mark it with a dot when you already know it is white. Dots are optional. A numbered cell can take a dot. The puzzle is finished when the shaded cells are that one set, even if some white cells are still blank. Play is 5×5 through 10×10, each at easy, medium, and hard. The daily puzzle is an 8×8 medium grid. People also look this up as kuromasu.
Hitori also keeps shaded cells from sharing a side, and keeps the white cells connected. There, the shaded cells are the duplicates. Here a number counts the white cells it can see.
- The number counts a view. A number counts every white cell it can see in a straight line up, down, left, and right, including itself. A shaded cell blocks the view. The count stops at the edge.
- The number stays white. The numbered cell itself stays white. A numbered cell can take a dot.
- Apart, and one white group. Shaded cells never share a side. They may touch at a corner. The white cells of the whole board share sides in one group.
- Dots are optional. A dot is a cell you already know is white. The puzzle is finished when the shaded cells are that one set, even if some white cells are still blank.
A finished grid is the shaded set. Dots are not required. White cells stay paper. The frame is the solved frame. The shades are the solved teal. Numbers stay, and they are teal#14b8a6, because none of them sit on a shade. The digits are centred. No dots. No yellow ring. No hint. A printed answer fills the shaded cells and leaves white cells blank. Dots are not printed. Numbers are kept, and a number on a shaded cell is printed in white. On this finished picture no number sits on a shade.
- Shade
- Dot
- Number
- Clash
Choose Shade or Dot under the board. Tap a cell, or drag across cells, to place that mark. Tap a cell that already has the mark to clear it. A cell with the other mark takes the new one when you tap it. A drag follows the first cell: it places the mark on empty cells along the path, or it clears when that cell already has the mark. With a mouse, right-click places a dot, or clears a dot that is already there. Arrow keys move and stop at the edge. The first arrow, when nothing is selected, selects the top-left cell. Space or Enter places the selected mark, or clears it when the cell already has that mark. S or 1 shades. X, D, E, or 2 places a dot. M switches Shade and Dot. Backspace, Delete, or 0 clears the cell. There is no cycle through the marks.
While the puzzle is unfinished, the line under the board reads: "Tap or drag to mark. Tap again to clear. M switches mode."
Press Hint for one step the rules already force, with a sentence saying why. Hint lights the cells it writes. Press Check when you want the board checked. A legal unfinished board gets "No mistakes so far. Keep going!" A broken board gets "A number is shaded, two shaded cells touch, a number sees the wrong count, or the white cells are split. Look for the marked cells." Hint on a broken board gets "This board has a mistake, so there is no hint yet." If Hint finds nothing on a legal board, it says "No forced cell from here. A shaded cell or a dot may be in the wrong place, so try Check or Undo." Undo and Redo step through the moves. Reset clears every shade and every dot you placed. The numbers stay. When the shaded cells are the unique set, the board turns teal. The dialog title is "Solved!" The dialog body, and the line under the board once the grid is solved, is "Every number sees that many white cells. Shaded cells stay apart, and the white cells stay connected." The Mistakes counter counts how many times Check found a broken board. It is not a score.
The ideas, in the order you can use them, are these. A shaded cell forces the cells beside it to stay white. A number can see only as far as its value, so the open cells on those lines stay white. A number that already sees its count shades the next cell on each open line. When only one direction is still open, that line has to be exactly this long. A cell that every remaining length sees through stays white. Medium grids look at the lengths that still add up, and at white cells that would split. Hard grids try the other mark on one cell and keep the mark that does not break the board. The button writes one of those ideas and stops.
A cell turns coral when a number is shaded, when two shaded cells share a side, when a number already sees too many white cells, when a number can no longer see enough, or when the white cells are split. With error highlighting off, none of that coral is drawn. The picture of a finished grid in this article leaves the white cells blank. A printed answer does the same.
- Undo
- Redo
- Reset
- Hint
- Check
Beside a shade
A shaded cell cannot touch another shaded cell, so the cells beside it stay white. A blank grid has no shade yet, so it does not open here. On the grid below, the number spoke before this press. The article still teaches the neighbour here.
Beside the shade Easy
A shaded cell cannot touch another shade along a side. The cells that share a side with it stay white. On this grid row 4 column 1 and row 4 column 4 have just been shaded. The press dots row 3 column 1, row 5 column 1, row 3 column 4, and row 5 column 4. Row 4 column 3 is already a dot, so it is not written again. Row 4 column 2 and row 4 column 5 are numbers, so they are already white. The four new dots sit above and below the two shades.
The sentence stays plural when the press writes one cell. On another grid, the shade at row 1 column 5 has one unknown neighbour to its left. The press dots row 1 column 4 only. Before that press, row 1 is blank, blank, blank, blank, shade. Row 2 is blank, blank, blank, dot, dot. Row 3 is blank, blank, dot, shade, blank. Row 4 is blank, blank, blank, dot, dot. Row 5 is blank, dot, shade, blank, dot. After the press the grid is still unfinished, with 14 cells still blank. The toast is still "This shaded cell cannot touch another shaded cell, so the cells beside it stay white." Hint on an easy grid still offers that dot. That press is not drawn.
The figure shows the board as it is when this press fires, including the dots and shades from the number.
Amber wash, a yellow border, and a yellow ring on the four new dots. Each is a centred muted-ink dot. The two shades stay ordinary violet, with no yellow ring. The earlier dots stay ordinary. The numbers stay ink, centred. The grid is still unfinished. Hint says "This shaded cell cannot touch another shaded cell, so the cells beside it stay white."
The number
Start with one number. When the open cells already make exactly that count, those cells stay white. When the number already sees enough, the next cell on each open line is shaded. When only one direction is still open, that line has to be exactly this long. A cell that every remaining length sees through stays white. The one open line is not on every easy grid. No 5×5 button press says it.
Only as far as the number Easy
A number counts itself, then white cells in four directions, until a shade or the edge. When the cells still open already make exactly that count, every one of them stays white. You do not get to choose which.
On a blank grid the 9 at row 1 column 2 can see eight cells besides itself, and no more. Up is the edge. Left is row 1 column 1. Right is row 1 column 3, row 1 column 4, and row 1 column 5. Down runs through the 6 at row 2 column 2 and the 6 at row 4 column 2, both already white because they are numbers, and the open cells on that line are row 3 column 2 and row 5 column 2. The longest view is exactly 9, so the press dots all six open cells. The other numbers on this blank board do not add a cell.
The toast is "This number can see only as far as its value, so every open cell on those lines stays white." A blank grid that can see exactly often opens here, for easy, medium, and hard. This grid does. The 9 stays ink. The board is not solved, so the number does not turn teal.
Amber, a yellow border, a yellow ring, and a centred muted-ink dot on those six cells. The 9 at row 1 column 2 stays ink, centred. It is not in the write, so it has no ring. Every other cell stays paper. The grid is still unfinished. Hint says "This number can see only as far as its value, so every open cell on those lines stays white."
Already enough Easy
Once a number already sees its count in white cells, the next cell on each open line is shaded. That shade stops the view.
On this grid the 6 at row 4 column 2 already sees six white cells. Up is row 3 column 2, the 6 at row 2 column 2, and the 9. Down is row 5 column 2, already a dot. Right has row 4 column 3 already a dot, so the next cell is row 4 column 4. Left is row 4 column 1, and that direction has no white cell yet, so the shade sits on row 4 column 1 itself. The press shades row 4 column 1 and row 4 column 4. It does not rewrite the dots it already counted.
The toast is "This number already sees enough white cells, so the next cell on each open line is shaded." On this grid the needed white is an earlier press. The article still teaches the finished count here, and the needed white later. The figure shows the board as it is when this press fires.
Many last presses in the set are this sentence, and they finish the grid. The live button skips that toast. This figure is an earlier press. It leaves the grid unfinished.
Violet shade and a yellow ring on row 4 column 1 and row 4 column 4. The 6 at row 4 column 2 stays ink. It is not in the write. The earlier dots stay ordinary. The digits stay centred. The grid is still unfinished. Hint says "This number already sees enough white cells, so the next cell on each open line is shaded."
One open line Easy
When a number has only one direction left, that line has to make up the rest of the count. The cells inside the length stay white. The cell where the length stops is shaded. One press writes both.
On this grid the 8 at row 1 column 6 is on the right edge, so right is closed, and up is the edge. Down already has five white cells: the dot at row 2 column 6, the 11 at row 3 column 6, and the dots at row 4 column 6, row 5 column 6, and row 6 column 6. The 11 is white because it is a number. It has no player dot. The 8 still needs two more cells, and the only open direction is left. The press dots row 1 column 5 and row 1 column 4, and it shades row 1 column 3. The shade is the lower index, so it is the first cell in the write. The sentence does not change because of that.
The toast is "Only one direction is still open, so that line has to be exactly this long." This is a medium grid, and the sentence is in the easy group. Hint on an easy grid still offers it. No 5×5 button press says it. Not every easy grid says it. On a 6×6 easy grid, the 4 at row 6 column 6 has only up still open. Left is already two white cells and then the shade at row 6 column 3. Right and down are the edge. The 4 already has three of its four, so the press shades row 4 column 6 and dots row 5 column 6. Before that press, row 1 is blank, blank, dot, shade, dot, blank. Row 2 is dot, dot, blank, dot, dot, dot. Row 3 is blank, dot, dot, dot, dot, blank. Row 4 is blank, blank, dot, dot, dot, blank. Row 5 is blank, blank, dot, dot, dot, blank. Row 6 is blank, dot, shade, blank, blank, blank. After the press the grid is still unfinished, with 14 cells still blank. That grid has a 10, so the digits are the smaller size. That press is not drawn.
The figure uses the smaller digit size, because of the 11. The 11 stays ink, with no dot and no ring.
Violet and a yellow ring on row 1 column 3. Amber, a yellow ring, and a centred muted-ink dot on row 1 column 4 and row 1 column 5. The earlier dots stay ordinary. The 8 and the 11 stay ink, centred. The grid is still unfinished. Hint says "Only one direction is still open, so that line has to be exactly this long."
Every way sees through it Easy
A number can often be made in more than one set of lengths. A cell that every remaining way sees through stays white. You do not yet choose which length it belongs to.
On this grid the 7 at row 5 column 3 still has two lengths up that can work, 2 and 4, and the lengths in between are not available. Both of those lengths see through row 4 column 3 and row 3 column 3. Right can be 0, 1, or 2, and that does not force a cell. Down is the edge. The press dots row 3 column 3 and row 4 column 3. The sentence stays singular.
The toast is "Every way to make this number sees through this cell, so the cell stays white." The 6 and the 5 on this board do not force those two cells. This press is the 7. On this grid the finished count is a later press. The article has already taught that count. The figure shows the board as it is when this press fires, which is after the opening view and before the two shades.
Amber, a yellow border, a yellow ring, and a centred muted-ink dot on row 3 column 3 and row 4 column 3. The 7 stays ink. The earlier dots stay ordinary. The digits stay centred. The grid is still unfinished. Hint says "Every way to make this number sees through this cell, so the cell stays white."
The lengths
List the lengths that can still add up to the number. A cell every remaining length stops on is shaded. When those lengths run without a gap, that is one sentence. When they skip a length, that is the other. An easy walk does not say either. Hint on an easy grid still offers the step.
Every way stops here Medium
The same list of lengths can force a shade. When every length that can still work stops on one cell, that cell is shaded. On this grid the lengths downward have no gap between them. The ones that survive all stop on the same cell.
On this grid the 6 at row 5 column 3 needs five cells besides itself. Left is already two white cells, and that is the only length left there. Up can be 0 or 3. Right can be 0 or 3. Down can be 0 or 1, with nothing skipped, and the only length that still fits the rest of the count is 0. Every remaining way stops on row 6 column 3. The press shades row 6 column 3. The 5 at row 6 column 1 sees that cell and does not force the shade.
The toast is "Every way to make this number stops on this cell, so it is shaded." This is the same grid as the one open line, four presses later. Row 1 of the figure already shows that result: the shade at row 1 column 3, and the dots at row 1 column 4 and row 1 column 5. The 8 has no dot. The article has already taught that line.
Only two grids in the set say this sentence. The other is a 9×9 hard grid. It says it twice. That grid is not drawn. Hint on an easy grid still offers this shade. No easy walk says it. No 5×5 walk says it.
Violet and a yellow ring on row 6 column 3 only. The shade at row 1 column 3 stays ordinary violet, with no ring. The 6 at row 5 column 3 stays ink. The 11 stays ink, with no dot. The digits are the smaller size, centred. The grid is still unfinished. Hint says "Every way to make this number stops on this cell, so it is shaded."
The lengths still add up Medium
Sometimes a direction could be long or short, and the lengths in between are not available. If every length that still adds up to the number stops on the same cell, that cell is shaded. The skipped lengths are why this is its own sentence.
On this grid the 4 at row 3 column 4 needs three cells besides itself. Left could be 0 or 3, and 1 and 2 are not available. Up, right, and down cannot all be 0 at once, so a left run of 3 does not fit. The only length left on that side is 0, and it stops on row 3 column 3. The press shades row 3 column 3.
The toast is "The lengths that still add up all stop on this cell, so it is shaded." If the same pass also shaded a cell whose lengths had no hole, the button would still use this sentence. This press is only the skipped length.
This is a medium grid. Hint on an easy grid still offers the shade. No easy walk says it. The grid opened on a view of fourteen dots. That opening is not drawn. The figure shows the board as it is when this press fires.
Violet and a yellow ring on row 3 column 3 only. The 4 at row 3 column 4 stays ink. The earlier dots stay ordinary. The digits stay centred. The grid is still unfinished. Hint says "The lengths that still add up all stop on this cell, so it is shaded."
The white cells
The white cells you have already marked have to end in one group. A blank cell can be the only path between two of them. Shading that cell would split them, so the cell stays white. Cells that cannot reach the white group would be shaded, with the sentence "These cells cannot reach the white group, so they are shaded." On these grids that second idea never writes. No figure. An easy walk does not say the split. Hint on an easy grid still offers it. Not every medium grid says it. Two of the three 5×5 medium grids finish before this sentence.
They would split Medium
The white cells you have already marked have to end in one group. A blank cell can be the only path between two of them. Shading that cell would split them, so the cell stays white.
On this grid row 4 column 1 is a dot, and row 5 column 2 is a dot. They meet through row 5 column 1, which is still blank. Row 4 column 2 is already shaded, and row 5 column 3 is already shaded. If row 3 column 1 were shaded, that pair could not reach the other white cells: the 4 at row 3 column 2, the dots along row 2, and the rest of the marked whites. The press dots row 3 column 1. It does not shade anything.
The toast is "The white cells would split without this cell, so it stays white." Those two 5×5 medium grids that finish first are not used here. This grid still opened on the try in the next section. This press comes later. The article has already taught the try. The last press on this grid finishes. It is not drawn.
Amber, a yellow border, a yellow ring, and a centred muted-ink dot on row 3 column 1. The 4 at row 3 column 2 stays ink. Row 4 column 1 and row 5 column 2 stay ordinary dots. Row 4 column 2 stays ordinary violet, with no ring. The digits stay centred. The grid is still unfinished. Hint says "The white cells would split without this cell, so it stays white."
One cell, both ways
Try the other mark on one cell. If one mark cannot be finished, keep the other. If both marks can be finished and they force the same mark on another cell, write that mark. The button has two sentences, so they have their own sections. An easy walk and a medium walk do not say either. Hint on an easy grid still offers the step. On these grids the agreement only writes a dot.
The other mark fails Hard
When the earlier sentences stop, try the other mark on one cell. Close the board from that mark, without a second try inside it. If the shade cannot be finished, the cell stays white. If the white mark cannot be finished, the cell is shaded. The press writes the mark that lives.
On a blank grid row 3 column 3 is still empty. A shade there cannot be finished. The cells beside it, row 2 column 3 and row 3 column 4, would have to stay white. The 6 at row 4 column 3 then sees exactly six cells up through that shade, so row 4 column 1, row 4 column 2, row 4 column 4, row 4 column 5, and row 5 column 3 stay white. The 3 at row 5 column 4 already sees four white cells, which is more than 3. A dot at row 3 column 3 does not break the board. The press dots row 3 column 3.
The toast is "Shading this cell cannot be finished, so it stays white." The same try can shade a cell. On this same grid, the next press finds that leaving row 3 column 4 white cannot be finished. The closure shades row 2 column 2, row 2 column 5, row 3 column 1, row 4 column 2, and row 4 column 5, dots the cells beside those shades, and then the 3 at row 5 column 4 already sees seven white cells. A shade at row 3 column 4 stays legal. The press shades row 3 column 4. Before that press the only mark is the dot at row 3 column 3. After it, the grid is still unfinished, with 23 cells still blank. The toast is "Leaving this cell white cannot be finished, so it is shaded." Row 3 column 5 is the 4, already white because it is a number. That press is not drawn.
This grid opens on the try, for easy, medium, and hard. The article still teaches the number first. The figure is the blank board. Easy walks and medium walks do not say this. Hint on an easy grid still offers it.
Amber, a yellow border, a yellow ring, and a centred muted-ink dot on row 3 column 3. No number sits on that cell. The 6 at row 4 column 3 and the 3 at row 5 column 4 stay ink. The digits stay centred. Every other cell stays paper. The grid is still unfinished. Hint says "Shading this cell cannot be finished, so it stays white."
Both ways agree Hard
Sometimes both marks on the cell under test can be finished, and both of them force the same mark on another cell. The press writes that other cell. It does not have to write the cell you tried.
On this grid the cell under test is row 2 column 1. It is not the cell the press writes. Leaving row 2 column 1 white forces a shade at row 5 column 1, and the cell beside that shade, row 5 column 2, stays white. Shading row 2 column 1 dots row 1 column 1, row 2 column 2, and row 3 column 1. The 8 at row 1 column 5 then already sees eight, so row 5 column 5 is shaded, and later the 3 at row 4 column 1 already sees itself, row 3 column 1, and row 5 column 1, so row 4 column 2 is shaded. The cell beside row 4 column 2 is row 5 column 2, which stays white. Both ways leave a dot at row 5 column 2. The press dots row 5 column 2 and nothing else.
The toast is "Both ways of marking the cell under test force the same mark here." On these grids that shared mark is always a dot. The other grid that says it is an 8×8 hard grid, and that write is a dot too. It is not drawn.
On this grid the agreement is the second press, and a try that dots row 3 column 3 is the third. The toast of that later try is "Shading this cell cannot be finished, so it stays white." That press is not drawn. The article still teaches the try first. The figure shows the board as it is when the agreement fires, which is after the opening needed white and before that later try.
An easy walk and a medium walk do not say this. Hint on an easy grid still offers the dot.
Amber, a yellow border, a yellow ring, and a centred muted-ink dot on row 5 column 2. No ring on row 2 column 1. The earlier dots stay ordinary. The 8, the 6, the 3, and the 5 stay ink, centred. The grid is still unfinished. Hint says "Both ways of marking the cell under test force the same mark here."
Common mistakes
Check paints a broken rule. Hint will not explain a board that is already broken. The toast is "This board has a mistake, so there is no hint yet." A wrong shade or a wrong dot can also sit there with no coral at all. Then Check says "No mistakes so far. Keep going!" and Hint still offers the next real step. The wrong mark stays unless that step writes the cell. A direct call on a broken board can still return a step, because a mark that disagrees with the solution is set aside for that computation. The button does not make that call. The figures do not draw it.
Five pictures, all on the same blank grid as the 9. No amber on the four broken ones. The quiet one shows the opening six dots, because the board is legal. Coral is the cells the rule names. A shaded number paints that cell, and the digit stays white. A shade that cuts a number off paints the number, not the shade. Two shades that share a side paint those two shades. A number that already sees too many white cells paints the number, not the dots.
Row 1 column 2 is shaded. That cell is coral, in the shade mix. The digit stays white. The 5 and the 7 are the same kind on their own. This picture uses the 9. Nothing is amber. Hint says "This board has a mistake, so there is no hint yet."
Row 1 column 3 is shaded, so the 9 can no longer see nine cells. The shade is not a number, and it does not touch another shade. Only the 9 is coral. That tile is coral-soft. The digit is coral mixed into the ink. The shade at row 1 column 3 stays ordinary violet. A shade at row 1 column 1 is the same kind. This picture uses row 1 column 3. Nothing is amber. Hint says "This board has a mistake, so there is no hint yet."
Row 2 column 4 and row 2 column 5 share a side. Neither is a number, and neither is a shade in the solution. Those two shades are coral, in the shade mix. The rest of the board stays paper. Nothing is amber. Hint says "This board has a mistake, so there is no hint yet."
Dots at row 1 column 5, row 2 column 5, row 3 column 5, row 4 column 4, and row 5 column 5 push the 5 at row 4 column 5 to six white cells: itself, and those five dots. Only the 5 is coral. That tile is coral-soft. The digit is coral mixed into the ink. The five dots stay muted ink, with no amber and no yellow ring. Row 4 column 4 is white in this picture and shaded in the solution. It is still not coral, because this rule paints the number. Nothing else is amber. Hint says "This board has a mistake, so there is no hint yet."
With error highlighting off, the shaded 9, the shade on the 9's line, the touching pair, and the 5 that sees too many paint nothing coral. A split of the white cells, with no blank path left between them, is not drawn here, and it can still occur. A full board that passes the checks you can see and still misses the shaded set is not drawn here, and it can still occur.
The shade at row 2 column 1 is white in the solution. It is not a number. It does not touch another shade. No number is cut off, and no number already sees too many. No coral. Check says "No mistakes so far. Keep going!" Hint still dots row 1 column 1, row 1 column 3, row 1 column 4, row 1 column 5, row 3 column 2, and row 5 column 2. The wrong shade is not among them, and it stays. Amber is allowed on those six dots, not on row 2 column 1.
A dot at row 2 column 3, which is shaded in the solution, is also quiet, and Hint still offers the same opening six dots. A dot on the correct white cell at row 1 column 1 is quiet, and the opening write simply omits that cell. That is not a broken board. Those dots are not drawn.
What to play next
Easy grids follow from one number at a time, plus the cells beside a shade. A number that can see only as far as its value, a number that already sees enough, sometimes one open line, and a cell every remaining length sees through. Start on a 5×5 easy grid. The 5×5 easy grids do not say the one open line. One 6×6 easy grid opens on the needed white and later says the one open line. Medium grids are built so the full colouring needs a length or a split. The button says that sentence when the shaded set is not already finished. Two of the three 5×5 medium grids finish before it. The daily puzzle is an 8×8 medium grid. Hard grids add the try. One 5×5 hard grid opens on the try. A second hard sentence writes a cell both ways agree on. On these grids that write is a dot. The cells that cannot reach the white group do not write on these grids.
- Easy5×5The number, the cells beside a shade, and the cell every length sees through. These grids do not say the one open line.Play 5×5 →
- Easy6×6Those sentences, and one grid opens on the needed white and later says the one open line.Play 6×6 →
- Medium6×6A length, after the earlier sentences. One of these grids says the stop with no hole.Play 6×6 →
- Medium8×8A length or a split, after the earlier sentences. This is the daily size.Play 8×8 →Today's daily →
- Hard5×5The try, after the earlier sentences. One grid in this set opens on it. One grid also says the agreement, and that write is a dot.Play 5×5 →
- Hard8×8The try, after the earlier sentences. One grid also says the agreement, and that write is a dot.Play 8×8 →
- Hard9×9The try, after the earlier sentences. One grid opens on the finished count. One grid says the stop with no hole.Play 9×9 →
A printed answer fills the shaded cells and leaves white cells blank. Dots are not printed. Numbers are kept. Four 5×5, 6×6, or 7×7 grids share a sheet. Two 8×8, 9×9, or 10×10 grids share a sheet. A 12×12 grid has the sheet to itself. 12×12 is print only, at easy, medium, and hard. The printable page is Kurodoko packs.
There is no guide-sized seed to open. The boards above are teaching boards.