Rules
Dominosa is a placement puzzle. The board is a tall grid of numbers. A domino covers two cells that share a side. Each pair of numbers appears exactly once, including two copies of the same number. On a 5×4 the numbers are 0 through 3, and each number appears five times. A larger grid uses a higher top number, and each number still appears once for every row. Every cell belongs to one domino. You can mark a boundary with a wall when you already know it is not a domino. You do not have to place every wall. An empty line is simply not a domino yet. The numbers are printed. You do not change them. The puzzle is finished when the dominoes are the one solution. Play and print are 5×4, 6×5, 7×6, 8×7, 9×8, 10×9, and 11×10, each at easy, medium, and hard. The daily puzzle is an 8×7 easy grid. People also look this up as a dominosa puzzle, a domino puzzle, or a printable dominosa puzzle.
- Each pair once. A domino covers two cells that share a side. Each pair of numbers appears exactly once, including two copies of the same number.
- Every cell. Every cell belongs to one domino. On a 5×4 the numbers are 0 through 3, and each number appears five times. A larger grid uses a higher top number.
- Walls are optional. A wall marks a boundary you have ruled out. You do not have to place every wall. An empty line is simply not a domino yet.
Ten dominoes. The other lines stay empty. The frame is the solved frame. The pills are the solved teal. Numbers are teal. No walls. No yellow ring. A printed answer outlines each domino, drops the line between the pair, keeps the numbers, and does not print walls.
- Domino
- Wall
- Number
- Clash
Choose Domino or Wall under the board. Tap the line between two cells to place the mark you picked. Tap that same mark again to clear it. An edge that already has the other mark takes the new one. You can also tap one cell and then a neighbour. A drag from one cell onto a neighbour does the same, and a longer stroke uses only that first step. With a mouse, right-click places a wall, including when Domino is selected. A second right-click leaves the wall in place. Tap that wall while Wall is selected to clear it. Right-click on a number does not place a wall. Arrow keys move the cell cursor and stop at the edge. The first arrow, when nothing is selected, selects the top-left cell. Hold Shift and press an arrow to place the active mark on that edge. M switches Domino and Wall. There is no key that cycles the marks.
The line under the board reads "Tap two neighbours or the line between them. Tap again to clear."
Press Hint for one step the rules already force, with a sentence saying why. Hint lights the cells of the edges it wrote. One press can place several walls. The sentence does not change. Press Check when you want the board checked. A legal unfinished board gets "No mistakes so far. Keep going!" A broken board gets "A pair is repeated, a cell is in two dominoes, or a number has nowhere to go." 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 domino from here. A mark may be wrong, so try Check or Undo." Undo and Redo step through the moves. Reset clears the marks you placed. The numbers stay. When the dominoes match, the board turns teal. The dialog title is "Solved!" The dialog body is "Every domino is placed once. Walls are not required." The line under the board once the grid is solved is "Every pair is placed once. Walls are optional." The Mistakes counter counts how many times Check found a broken board. It is not a score.
A cell turns coral when a number has nowhere to go, or when a cell sits in two dominoes. A repeated pair, and a finished tiling that is not the solution, turn the two cells and the line between them coral. With error highlighting off, none of that coral is drawn. The picture of a finished grid in this article draws the dominoes and leaves every other line empty.
The pair
Look for a pair that can sit in only one place, and lay that domino. Then look for a cell with only one neighbour left. A blank grid in this set opens on the pair, never on the neighbour. Three of the four 5×4 easy grids finish without the neighbour. The grid in the next section is the one that says it.
This pair fits in only one place Easy
A pair that can sit in only one place is placed there. On this blank grid the two 2s between row 3 column 2 and row 4 column 2 are the only 2-2. The press places that domino. The 0 and the 3 between row 3 column 3 and row 3 column 4 are also the only 0-3. The button writes one pair and stops, and it writes the 2-2 first. Hint says "This pair fits in only one place."
The rings sit on row 3 column 2 and row 4 column 2. The new pill is the ordinary open pill. The press does not also draw the walls around those two cells. The grid is still unfinished. This is the opening press. Easy, medium, and hard all give this hint, and so does a label outside those three. The last press of this grid is also this sentence, the 3-3 at the top left, and that press finishes the grid, so the button does not show the sentence. That press is not drawn. The next press places the 1-2 between row 1 column 3 and row 1 column 4 by this same sentence. It does not finish. That press is not drawn.
The 2-2 is the new open pill. Yellow rings sit on its two cells. The pill itself stays the ordinary open pill. No wall. The grid is still unfinished. Hint says "This pair fits in only one place."
Only one neighbour Easy
A cell with only one neighbour left has to join that neighbour. On this grid the 0-0 between row 2 column 1 and row 2 column 2 is already placed, and the 3-3 between row 4 column 4 and row 5 column 4 is already placed. The 3 at row 1 column 1 cannot join the cell below it, because that cell is in the 0-0. Its only neighbour is the 2 at row 1 column 2. The press places that 3-2. Hint says "This cell has only one neighbour it can join."
The rings sit on row 1 column 1 and row 1 column 2. The two older pills have no ring. The new pill is the ordinary open pill. The grid is still unfinished. This is not the blank board. A blank grid in this set does not open here. The grid in the previous section never says this sentence. Three of the four 5×4 easy grids finish without it. Easy, medium, and hard all give this hint, and so does a label outside those three. The next press on this grid is this same sentence again, the 3 at row 3 column 1 joining the 0 at row 4 column 1. It does not finish. That press is not drawn.
The new 3-2 is the ordinary open pill, with yellow rings on row 1 column 1 and row 1 column 2. The 0-0 and the 3-3 stay ordinary, with no ring. The grid is still unfinished. Hint says "This cell has only one neighbour it can join."
The same pair
When every way to cover a cell is the same pair, that pair cannot sit anywhere else. When every remaining place for a pair covers one cell, that cell cannot take another pair. A placement that would leave a region with an odd number of cells is removed, because a domino covers two cells. The 5×4 walks in this set never write the odd region. The picture is a 6×5. A medium grid can still open on a pair that fits in one place. One 5×4 medium grid opens on the same pair.
Removed everywhere else Medium
When every way to cover a cell uses the same pair, that pair is removed everywhere else. On this blank grid the 0 at row 5 column 3 has three neighbours, and each of them is a 1: above it, to its left, and to its right. Every cover of that 0 is a 0-1. The other 0-1 spots are between row 2 column 1 and row 2 column 2, and between row 2 column 2 and row 2 column 3. The press walls those two lines. The three lines around the bottom 0 stay empty. Hint says "Every way to cover this cell is the same pair, so that pair is removed everywhere else."
The rings sit on row 2 column 1, row 2 column 2, and row 2 column 3, the cells of the two walls. The 0 at row 5 column 3 has no ring. The walls are ordinary wall ink. The sentence stays the same when the press writes one wall. On a later hard grid, the 0 at row 5 column 4 can only join a 1, so the other 0-1, between row 3 column 3 and row 3 column 4, is the one wall. Before that press the only mark is the 0-0 between row 1 column 4 and row 2 column 4. That one wall is not drawn. The grid there is still unfinished, and the toast is still the same sentence. This grid opens here. The article still taught the one place and the only neighbour first. No easy walk says this sentence. Easy, medium, and hard all give this hint, and so does a label outside those three. The press does not finish the grid.
Two walls in row 2. Yellow rings sit on row 2 column 1, row 2 column 2, and row 2 column 3. The 0 at row 5 column 3 has no ring. The walls stay ordinary wall ink. The grid is still unfinished. Hint says "Every way to cover this cell is the same pair, so that pair is removed everywhere else."
Every place covers this cell Medium
When every remaining place for a pair covers one cell, that cell is in the pair, so it cannot take another pair. On this grid the 2-2 between row 2 column 2 and row 3 column 2 is already placed. The 0-1 can still sit in two places, and both of them cover the 0 at row 2 column 4: up to the 1 at row 1 column 4, and down to the 1 at row 3 column 4. The other line out of that 0 is the 0-0 to its left. The press walls that line, between row 2 column 3 and row 2 column 4. The two 0-1 lines stay empty. Hint says "Every remaining place for this pair covers this cell, so the cell cannot take another pair."
The rings sit on row 2 column 3 and row 2 column 4. The wall is ordinary wall ink. The older 2-2 has no ring. The grid is still unfinished. This is not the opening. The opening was the 2-2. One 6×5 hard grid does open on this sentence. That grid is not drawn. No easy walk says this sentence. Easy, medium, and hard all give this hint, and so does a label outside those three.
One wall between row 2 column 3 and row 2 column 4. Yellow rings sit on those two cells. The 2-2 stays ordinary, with no ring. The wall stays ordinary wall ink. The grid is still unfinished. Hint says "Every remaining place for this pair covers this cell, so the cell cannot take another pair."
An odd region Medium
A domino covers two cells, so a region with an odd number of cells cannot be tiled. On this grid two dominoes are already placed: the 3-3 between row 3 column 1 and row 3 column 2, and the 2-1 between row 2 column 3 and row 3 column 3. Three walls are already drawn, and they are not this lesson: between row 1 column 4 and row 2 column 4, between row 5 column 3 and row 5 column 4, and between row 5 column 3 and row 6 column 3. Joining the 2 at row 1 column 2 to the 4 at row 1 column 3 would leave three cells on their own: the 0 at row 1 column 1, the 4 at row 2 column 1, and the 2 at row 2 column 2. Three is odd. Those cells only touch each other once that 2-4 is placed, because the cells below them are already in the 3-3 and the cell to the right of the 2 is already in the 2-1. The press walls the 2-4. Hint says "This placement would leave an odd region, so it is removed."
The rings sit on row 1 column 2 and row 1 column 3. The new wall is ordinary wall ink. The older dominoes and the older walls have no ring. The three cells are named in the sentence. They are not washed. The rest of the open cells are also an odd count, because the open cells were even and three were split off. Teach the three. The grid is still unfinished. The 5×4 walks in this set never write this sentence. A 5×4 can still have an odd pocket. The picture is a 6×5. No easy walk says it. An easy label on this picture still returns it. This grid's earlier presses were two pairs that fit in one place and two shared-cell walls. The article still taught those first. Another 6×5 medium grid walls the line between row 1 column 4 and row 1 column 5 by this same sentence. The odd pocket there is seven cells. That press is not drawn.
One new wall between row 1 column 2 and row 1 column 3. Yellow rings sit on those two cells only. The 3-3, the 2-1, and the three older walls stay ordinary. The three cells in the pocket are not washed. The grid is still unfinished. Hint says "This placement would leave an odd region, so it is removed."
One number
Two or three cells of one number can already be holding the only pairs they can use. Those pairs are then removed where they miss that set. The rings sit on the removed edge, not on the cells of that number. No easy walk and no medium walk say this. The picture is a 5×4 hard grid, after earlier sentences.
Room for these pairs Hard
Cells of one number can have only a few pairs left between them. On this grid the 0-0 between row 1 column 4 and row 2 column 4 is already placed, the 1-1 between row 3 column 4 and row 4 column 4 is already placed, and the 1-0 between row 5 column 3 and row 5 column 4 is already placed. One wall is already drawn, between row 3 column 3 and row 3 column 4. The 2 at row 1 column 1 can join the 1 beside it or the 2 below it. The 2 at row 1 column 3 can join that same 1 or the 2 below it. The cell to its right is already in the 0-0. Those two 2s, and only the pairs 1-2 and 2-2, use each other up. The other 1-2, between row 5 column 1 and row 5 column 2, is walled. Hint says "These cells of one number only have room for this set of pairs."
The rings sit on row 5 column 1 and row 5 column 2. The two 2s in the top row have no ring. The new wall is ordinary wall ink. The older pills and the older wall have no ring. The grid is still unfinished. No easy walk and no medium walk say this sentence. An easy label on this picture still returns it. The article still taught the pair first. On this grid the same-pair wall, the only neighbour, and two pairs that fit in one place came before this press. A 6×5 hard grid can write two walls in one press of this sentence. That press is not drawn. The sentence does not change.
One wall between row 5 column 1 and row 5 column 2. Yellow rings sit on those two cells only. The two 2s in the top row have no ring. The older pills and the wall in row 3 stay ordinary. The grid is still unfinished. Hint says "These cells of one number only have room for this set of pairs."
One cell, both ways
When a pair, or a cell, has two ways left, try each way. If one way cannot be finished, place the other. If both ways can be finished and they force the same domino, the button can place that domino. On these grids that second sentence never writes. The button does not hide the first sentence on an easy label. The article still teaches the pair first. One 5×4 hard grid opens on the other side. The picture here does not.
The other side Hard
When a pair has two places left, try each place. On this grid the 3-3 between row 1 column 3 and row 1 column 4 is already placed, and the 2-0 between row 3 column 3 and row 4 column 3 is already placed. The 0-0 can still sit at the top left, between row 1 column 1 and row 2 column 1, or between row 2 column 3 and row 2 column 4. Try the top left. The 0 at row 2 column 3 then has only the 1 on its left, because the cells above it and below it are already covered and the 0-0 on its right is the pair you just used. That 0-1 is placed, between row 2 column 2 and row 2 column 3. The 2 at row 1 column 2 is then boxed in: the 0 on its left is taken, the 3-3 on its right is already placed, and the 1 below it has just been taken. That 2 has nowhere to go. The top-left 0-0 is wrong, so the other 0-0 is placed, between row 2 column 3 and row 2 column 4. Hint says "The other side contradicts the board, so this domino is placed."
The rings sit on row 2 column 3 and row 2 column 4. The new pill is the ordinary open pill. The two older pills have no ring. The grid is still unfinished. No easy walk and no medium walk say this sentence. An easy label on this picture still returns it. One 5×4 hard grid opens on this sentence, placing the domino between row 4 column 3 and row 5 column 3 on a blank board. That opening is not drawn. The article still shows the two earlier dominoes first.
The button can also say "Both sides force this same domino." That is the case where both places can be finished, and they force one more domino that is the same either way. On these grids that sentence never writes. There is no picture of it here. The path can still occur.
The new 0-0 is the ordinary open pill, with yellow rings on row 2 column 3 and row 2 column 4. The 3-3 and the 2-0 stay ordinary, with no ring. The grid is still unfinished. Hint says "The other side contradicts the board, so this domino is placed."
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 domino or a wrong wall can also sit there with no coral at all. Then Check says "No mistakes so far. Keep going!" If the wrong mark did not remove the next step, Hint still offers that step on the board as it stands. The wrong mark stays unless that step writes the edge. If the wrong mark removed the only step, Hint says "No forced domino from here. A mark may be wrong, so try Check or Undo." A wrong mark is not set aside for the computation. The button does not call the hint on a broken board. The figures of a broken board do not draw a ring.
Three pictures, all on the blank grid from the first section. Coral is the cell the rule names. A number with nowhere to go paints that cell. The domino that trapped it stays an ordinary pill. A tap that joins a cell already in a domino clears the older domino, so you cannot tap a cell into two dominoes. Check's sentence still names "a cell is in two dominoes" for a saved board that holds both. A repeated pair, and a finished tiling that is not the solution, can still turn two cells and the line between them coral. Those pictures are not drawn here. The path can still occur.
A domino between row 1 column 2 and row 1 column 3 covers the cell beside the corner 3, and it uses the 3-1 the corner would need for the 1 below it. The 3 at row 1 column 1 is coral. The wrong pill stays the ordinary open pill. No yellow ring. Hint says "This board has a mistake, so there is no hint yet." The same kind of trap, not drawn here, paints row 1 column 2, row 4 column 1, or row 5 column 2.
The 2 and the 0 between row 1 column 4 and row 2 column 4 are a domino. That pair is not the solution, and it does not trap a number. No coral. Check says "No mistakes so far. Keep going!" Hint still places the opening 2-2, with yellow rings on row 3 column 2 and row 4 column 2. The wrong pill stays ordinary, with no ring and no coral. The picture is after that press. The wrong domino remains. A wall on the correct 3-3 at the top left is also quiet, and the hint is the same 2-2. A correct 3-3 the button did not ask for is quiet too, and the opening write is still the 2-2. That is not a broken board. Those marks are not drawn.
The wall rules out the only place that pair can sit. No number is trapped yet, because those two 2s still have other neighbours. No coral. No yellow ring. The wall is ordinary wall ink. Check says "No mistakes so far. Keep going!" Hint says "No forced domino from here. A mark may be wrong, so try Check or Undo." A wall on the only 0-3, between row 3 column 3 and row 3 column 4, is the same kind. That wall is not drawn.
What to play next
Easy grids follow from one forced placement. A pair that fits in only one place is laid. A cell with only one neighbour joins that neighbour. The 5×4 easy grids in this set often finish from the pair alone. One of them does say the only neighbour. Start on a 5×4 easy grid, or on the daily 8×7 easy grid. Medium grids add the pair that is removed everywhere else, the cell every remaining place covers, and, from 6×5, the odd region. A medium grid can still open on a pair that fits in one place. One 5×4 medium grid opens on the same pair. The 5×4 walks in this set finish before the odd region. Hard grids add the cells of one number, and the look at both sides. Both sides forcing the same domino does not come up on these grids. A hard grid can still open on an earlier sentence. One 5×4 hard grid opens on the other side.
A printed answer outlines each domino and leaves the other lines empty. Walls are not printed. Numbers are kept. Four 5×4, 6×5, or 7×6 grids share a sheet. Two 8×7, 9×8, or 10×9 grids share a sheet. An 11×10 grid has the sheet to itself. The printable page is Dominosa packs.
- Easy5×4The pair that fits in one place. Three of these four grids finish before the only neighbour.Play 5×4 →
- Medium5×4The same pair, and the cell every remaining place covers. These grids finish before the odd region. One of them opens on the same pair.Play 5×4 →
- Hard5×4The cells of one number, on one grid, and the other side. One grid opens on the other side.Play 5×4 →
There is no guide-sized seed to open. The boards above are teaching boards.