How to Play the Sliding Puzzle (15 Puzzle)
The sliding puzzle is a tray of numbered square tiles with one gap. The 4×4 version, with tiles 1 to 15, is the famous 15 puzzle, a craze in the 1880s. In Chinese it's called 数字华容道 ("number Huarong Road"), after the older sliding-block puzzle.
The goal
Slide the tiles until they read in order, left to right and top to bottom, with the gap in the bottom right corner:
| 1 | 2 | 3 | 4 |
| 5 | 6 | 7 | 8 |
| 9 | 10 | 11 | 12 |
| 13 | 14 | 15 |
Moving
- Tap a tile next to the gap to slide it into the gap.
- Tap a tile further along the same row or column as the gap to slide it and every tile between it and the gap, in one go.
- With a keyboard, the arrow keys push the tile beside the gap in that direction.
- Every tile that moves counts as one move.
Sizes
- 3×3 (the 8 puzzle): quick, good for learning.
- 4×4 (the 15 puzzle): the classic.
- 5×5 (the 24 puzzle): long, for when you've got the method down.
Solvable boards only
If you take a solved puzzle and swap two tiles, it can never be solved by sliding. That's true of exactly half of all possible arrangements. kawu only ever deals boards that can be solved.
Hints, undo and the daily puzzle
The hint shows the next move of a solution that works row by row, the way people solve it. Undo takes back a slide. The daily puzzle is the same 4×4 board for everyone, every day.
Frequently asked questions
Is every 15 puzzle solvable?
No. Exactly half of all arrangements of the tiles can't be solved: swapping any two tiles of a solved puzzle makes it impossible. Every board kawu deals is solvable.
What's the fewest moves to solve a 15 puzzle?
Any solvable 4×4 position can be solved in at most 80 single-tile moves. Most random positions need between 40 and 60 with perfect play; people usually take more.
Last updated 2026-10-19