Play Mosaic Puzzle Online
Shade cells so every numbered clue matches the count of filled cells in its 3×3 neighbourhood. Pure logic — no guessing required!
Created by Brian Hamilton
Tap to fill — tap again to mark empty — tap once more to clear
How to play Mosaic
Fill in squares to reveal a picture. Each number says how many squares are filled in the 3×3 block centred on it.
- That block includes the numbered square itself, which may be filled or empty like any other.
- At the edges the block is smaller: a clue on an edge sees six squares, and one in a corner sees four.
- Squares with no number are still counted by any clue near enough to see them.
- Every puzzle has exactly one solution and never needs a guess.
Controls: click a square to fill it, click again to mark it as definitely empty, and a third time to clear it. Check highlights any clue that is not satisfied.
A clue counts its own square too
This is the detail that trips up almost everyone arriving from Minesweeper. A Mosaic clue counts the filled squares in the 3×3 block centred on it, and that block includes the square the number is sitting in.
So a numbered square is not a wall or a marker to be worked around. It is an ordinary square that might be filled or empty like any other, and part of what its own number is counting.
The block shrinks at the edges. A clue in the middle sees nine squares, one on an edge sees six, and one in a corner sees four — which changes what each value means. A 4 in the middle is unremarkable; a 4 in a corner fills every square it can see.
| Position | Squares seen | Range | Settles everything at |
|---|---|---|---|
| Middle | 9 | 0–9 | 0 or 9 |
| Edge | 6 | 0–6 | 0 or 6 |
| Corner | 4 | 0–4 | 0 or 4 |
Those decisive clues barely ever appear
A 0 empties its block and a full count fills it, and both are lovely when you find one. Counting them on real boards is sobering.
Across generated 7×7 boards, a clue that settles its whole block appears about once per puzzle — roughly 2–4% of the clues shown.
The other classic move fares no better. Two neighbouring clues differing by 3 pin six squares at once, and that turns up about once every five boards.
Mosaic has no reliable killer pattern, and looking for one is the main reason people stall. What it has instead is overlap.
Every square is watched by several clues at once
A square is counted by every clue whose block covers it — so a square in the middle of the grid is described by up to nine different numbers. That is the structural fact that makes the puzzle work despite weak individual clues.
| Difficulty | Clues per square | Squares with no clue watching |
|---|---|---|
| Easy | 4.8 | 0% |
| Medium | 3.5 | 0% |
| Hard | 3.2 | 0% |
Even on hard, no square is ever left unwatched, and the typical square is described by three or four numbers pulling on it from different directions. A clue that cannot decide anything by itself still narrows what its neighbours can mean.
Compare neighbours rather than solving them
The productive technique follows directly. Two clues side by side see blocks that overlap in all but one column each, so subtracting them describes only those two outer columns.
The same works vertically, and with any difference, not just the extreme one. A difference of 2 between neighbours does not settle six squares, but it still tells you something no single clue could.
A worked board
Note how many of the numbers end up sitting on filled squares. If you have been treating the numbered cells as fixed background, that is the habit to break first.
Where solvers get stuck
Forgetting the clue counts itself. The single commonest error, and it makes every deduction off by one in the same direction.
Working one clue at a time. Most clues cannot be resolved alone. Progress comes from holding two overlapping clues in view together and asking what their difference says.
Not marking squares as empty. A square you have ruled out is what lets the next clue tip over. Filling is only half the notation.
Two things you can check about these puzzles
Every puzzle has exactly one solution, and it is verified twice. A board begins with a number in every cell, then clues are removed one at a time, each removal kept only if a solver confirms a single solution still remains. The finished board is then checked once more before it is offered, so a puzzle that slipped through the first pass is discarded rather than shipped.
Difficulty is the number of clues left, not the picture. On a 7×7 the generator leaves about 32 clues on Easy, 23 on Medium and 22 on Hard, out of 49. The picture underneath is random either way — roughly 35–65% of squares filled — so a hard board is not a more intricate image, just a sparser set of numbers describing it.
Mosaic, Fill-a-Pix and Mosaik
The puzzle is best known as Fill-a-Pix, the name used by Conceptis, which popularised it. You will also find it as Mosaic, Mosaik, Nurie-Puzzle and Count and Darken.
It is often described as Minesweeper without the guessing, and the comparison is fair as far as the counting goes — but the two differ on exactly the point that matters here. Minesweeper numbers sit on safe squares and count only their neighbours; a Mosaic clue counts its own square as well, and the aim is to reveal a picture rather than avoid a loss.
More picture puzzles
If you like deducing an image from numbers, try these: