Divide the entire number grid into domino tiles. For example, a 4×5 grid must be split into exactly 10 dominoes: [0|0], [0|1], [0|2], [0|3], [1|1], [1|2], [1|3], [2|2], [2|3], [3|3].
How to Play
Tap between two adjacent cells to pair them as a domino.
Tap an existing domino again to unpair it.
Turn on X-mark mode to mark 'these two cells are NOT a pair'. Useful for elimination.
Rule 1: Unique Pairs
Each number combination can only appear once in the entire puzzle. If you've placed a [2|3] domino, no other [2|3] can exist.
Rule 2: All Cells Covered
Every cell must belong to exactly one domino — no gaps and no overlaps allowed.
Completed Example
A domino pairs two horizontally or vertically adjacent cells. For example, if cells show '2' and '5' side by side, they form a [2|5] domino.
Each number pair appears exactly once. If you've already placed a [1|3] domino, no other pair of cells can form another [1|3].
Every cell must belong to exactly one domino — no gaps and no overlaps allowed.
Tip
Key strategy: If a number pair (e.g. [0|3]) appears adjacent in only one place on the grid, that domino's position is certain. Find these 'forced' dominoes first.
Use the reference grid at the bottom (mobile) or side (desktop). Dominoes without a ✓ mark haven't been placed yet.
Use X marks to eliminate impossible pairs first — this narrows down the remaining possibilities quickly.
Dominosa puzzles train combinatorial reasoning. Systematic elimination is a core deductive reasoning skill linked to prefrontal cortex activation.
Goel, V. & Dolan, R.J. (2004). Differential involvement of left prefrontal cortex in inductive and deductive reasoning. Cognition, 93(3), B109-B121.
Ferreira, N., et al. (2015). Sudoku — a brain-teaser or a mental health aid? PLOS ONE, 10(3), e0120548.