What is the 15 puzzle?
The 15 puzzle is a sliding puzzle on a four-by-four frame. Fifteen tiles numbered 1 to 15 fill all but one square, and the empty square is the only room you have to manoeuvre. Sliding a tile that sits next to the gap moves it into the gap and leaves a new gap behind — there is no lifting tiles out, so every rearrangement has to flow through that single hole.
The goal is to slide the tiles until they read in order, row by row, with the empty square resting in the bottom-right corner. Reaching it from a thorough scramble can take dozens of moves and a clear plan, because fixing the last tiles without disturbing the first is the real art of the puzzle.
- A four-by-four frame holds 15 tiles and one empty square.
- Only a tile beside the gap can move, and it slides into the gap.
- Order the tiles 1 to 15 with the gap in the bottom-right.
- Nothing can be lifted out — every move goes through the hole.
- Larger grids simply add more tiles and the same rule.
How to play here
Tap any tile that shares a row or column with the empty square and the whole line slides toward the gap — tap the tile right next to the hole to move one, or a tile further along to slide several at once. On a keyboard the arrow keys slide a single neighbouring tile into the space.
The counters at the top track your moves and your time, and the board saves in your browser so a half-finished puzzle is waiting when you come back. Press Shuffle for a fresh scramble at any time, or switch grid size with the difficulty buttons.
- Tap a tile in the gap's row or column to slide the line.
- Tap next to the hole to move one tile, further to move several.
- Arrow keys slide a single tile on desktop.
- Moves and timer track your solve; progress saves locally.
- Shuffle restarts; the difficulty buttons change the grid.
A solving strategy
Solve the board in layers rather than chasing tiles at random. Place the top row first, then the left column, and the puzzle shrinks to a smaller one below and to the right; repeat until only a two-by-two corner is left, which you finish by rotating the three tiles around the gap.
The fiddly part of each row is the last two tiles. Rather than forcing them in one at a time, set them up in a little rotation: park the final tile just below its home, bring its partner into the corner, then cycle them into place together. Once a row or column is solved, keep the gap out of it so your finished work stays put.
- Complete the top row, then the left column, then recurse.
- Work down to a two-by-two and rotate it home.
- Place a row's last two tiles together, not one by one.
- Keep the gap away from rows and columns you have finished.
- Think a few slides ahead — every move trades one tile for another.
History of the 15 puzzle
The 15 puzzle appeared in the 1870s and set off a craze in 1880 that swept newspapers and parlours on both sides of the Atlantic. The puzzle maker Noyes Chapman is generally credited with its invention, and it has been a staple of pockets and desks ever since.
Its fame grew when Sam Loyd publicised a challenge starting from the solved board with only tiles 14 and 15 swapped, offering a large cash prize for a solution. No one ever claimed it, because that position is one of the unsolvable half — the puzzle that launched the craze also became an early popular lesson in the mathematics of parity.
Difficulty levels and why play online
Easy is the three-by-three eight puzzle, a gentle warm-up; Medium is the classic four-by-four fifteen puzzle; Hard steps up to a five-by-five with 24 tiles; and Expert fills a six-by-six frame with 35 tiles for a long, satisfying solve.
Playing online removes the only real frustrations of the physical toy: the tiles never jam, the scramble is guaranteed solvable, and the move counter lets you chase a tidier solution each time. The timer and local save mean you can pick up a tough board exactly where you left it.
- Easy: a 3x3 board (the 8 puzzle).
- Medium: the classic 4x4 board (the 15 puzzle).
- Hard: a 5x5 board with 24 tiles.
- Expert: a 6x6 board with 35 tiles.