About the Sliding Puzzle
The 15 puzzle is a classic sliding tile puzzle invented in the 1870s. Fifteen numbered tiles sit in a 4×4 frame with one empty space; slide tiles into the gap until they read 1 to 15 in order. Our shuffle always produces a solvable arrangement, so every game can be finished.
How to solve a sliding puzzle
The 15 puzzle looks like it needs cleverness, but it is really a fixed procedure. Solving it in a set order stops later moves from undoing earlier ones.
- Finish the top row first — tiles 1, 2, 3 and 4 — then never disturb it again.
- Then the left column, tiles 5, 9 and 13. You are now solving a smaller 3x3 puzzle in the corner that is left.
- Repeat. Complete the next row, then the next column, until only a 2x2 corner remains, which resolves with simple rotation.
- Place the last two of any row together. Setting them one above the other and rotating them into place avoids the trap of putting one in and pushing the other out.
Only half of all possible arrangements of the tiles can be solved at all, which is why the shuffle matters — see below.
Frequently asked questions
Is every shuffle solvable?
Yes. The board is scrambled by making many random legal slides from the solved state, which can never create an unsolvable arrangement.
How is my best score measured?
By the fewest moves to solve. Your best is saved locally in your browser. The timer is shown for reference and to help you race yourself.
Why can only half the arrangements be solved?
Every legal slide changes the arrangement in a way that preserves a mathematical property called parity. Positions with the wrong parity simply cannot be reached, no matter how many moves you make — which is why the shuffle has to be generated carefully rather than at random.
Is there a fastest possible solution?
Yes. Any solvable 15 puzzle can be finished in at most 80 moves with perfect play. Solving it row by row takes many more than that, but it is a method a person can actually hold in their head.
Does it matter how fast I slide?
No. Nothing is timed against you mid-puzzle, so the count of moves is what your result reflects. Thinking before sliding costs nothing.