What is Dominosa?
Dominosa is a pencil-and-paper logic puzzle built around a standard set of dominoes. A double-six set, for example, contains 28 dominoes: every unordered pair of numbers from 0 to 6, including the seven doubles. Laid two cells per domino, those 28 tiles fill a grid 8 cells wide and 7 cells tall.
In the puzzle the dominoes have already been shuffled and laid down, but their dividing lines have been erased — all you see is the grid of numbers. Your job is to redraw the lines so that every cell belongs to exactly one domino and no domino is repeated.
- The grid holds a full set of dominoes with the borders removed.
- Split the grid into 1x2 dominoes, horizontal or vertical.
- Each cell belongs to exactly one domino.
- Every domino of the set appears exactly once — no repeats.
- A well-made puzzle has a single solution and needs no guessing.
How to play Dominosa here
There are no numbers to enter — the numbers are given. Instead you mark which neighbouring cells are joined into a single domino. Tap a number to select it, then tap an adjacent number to pair them; tap the same domino again to break it apart.
Because each cell can only belong to one domino, joining two cells automatically frees any earlier link on either of them. Place dominoes you are sure of first, and the rest of the grid steadily narrows down around them.
- Tap a cell, then tap a neighbour to join them as a domino.
- Tap a joined pair again to separate it.
- Wrong dominoes are highlighted so you can correct them.
- Use Hint to place one correct domino, or Clear to start the layout again.
- Solve reveals the full set when you want to check your work.
The core technique: one place only
The whole puzzle turns on a single idea. Since each domino appears exactly once, look for a pair of numbers — say 3 and 5 — that can be joined in only one spot anywhere on the grid. That domino is forced, so you can draw it immediately.
Placing one forced domino often creates the next. Once a 3-5 is fixed, the cells around it lose options, which can leave another pair with just one legal home. A keen Dominosa solver hunts continuously for these 'only one place' dominoes.
More ways to deduce
Edges and corners are friendly starting points because a corner cell has only two neighbours, so it can join in at most two ways. Doubles like 4-4 are worth scanning for too: a double can only be placed where two equal numbers sit side by side.
Later in the solve, switch to elimination. If a cell can only be covered by joining it one way — because its other neighbours are already taken — that domino is forced even if its pair could fit elsewhere in theory. Balancing 'this pair fits only here' against 'this cell can only join there' is the rhythm of a good Dominosa.
Difficulty levels and why play online
Easy Dominosa uses a smaller double-five set, so the grid is compact and the forced dominoes are easy to spot. Medium is the classic double-six, while Hard and Expert move up to double-seven and double-eight, where the larger grids hide longer chains of deduction.
Playing online keeps the bookkeeping effortless: joined cells snap together into clean tiles, wrong dominoes turn red, and your progress saves locally in your browser. Every grid is checked for a single solution, so a Dominosa always rewards patient pairing over guesswork.
- Easy: a compact double-five set to learn the idea.
- Medium: the classic double-six on an 8x7 grid.
- Hard: a double-seven set with longer deductions.
- Expert: a large double-eight grid for seasoned solvers.