Is every slide puzzle solvable?
Here is a fact that surprises many players: some slide puzzle layouts are mathematically impossible. Luckily, you will never meet one here.
The parity rule
Every arrangement of a slide puzzle falls into one of two families based on a property called parity. Only one family can be sorted into order. Because a random shuffle picks between them roughly evenly, about half of all truly random layouts have no solution at all.
Why our boards always work
Rather than shuffle blindly, we scramble by making many legal moves from a solved board. That guarantees the result stays in the solvable family, so every puzzle you get here can be finished. You never have to worry that the game handed you a dead board.
What this means for you
If a slide puzzle feels impossible, it is a planning challenge, not a broken one, and our solving guide can help. This idea of solvable versus impossible layouts also shows up in other games, as our page on whether a puzzle can be unsolvable describes.
Related questions
What is a slide puzzle?
A slide puzzle is a grid of numbered tiles with one empty gap. You slide neighbouring tiles into that gap, one at a time, until the numbers sit in order. Common sizes are 3x3, 4x4 and 5x5, with the 4x4 version known as the famous 15 puzzle.
How do you solve a 15 puzzle?
Solve a 15 puzzle in layers. Finish the top row first, then the left column, which shrinks the puzzle to a smaller grid. Repeat until only a 2x2 block remains, which you rotate into place. Handling the last two tiles of each row with a small rotation is the key trick.
Can a puzzle be unsolvable?
In theory yes, some arrangements genuinely have no solution, such as certain random slide puzzle layouts blocked by parity. But a well-designed puzzle always has an answer by definition. On Puzzle.now, every board we hand you is guaranteed solvable, so you can always finish.