The 15 Puzzle is the sliding tile game that has been circulating since 1878: fifteen numbered tiles in a four-by-four frame, one empty square, and the job of working the numbers back into order. Nothing is hidden and nothing is random once the board is set, which is what makes it a genuine thinking puzzle rather than a test of reflexes. The difficulty comes from the single gap. Every tile you want to move has to be walked around the board one step at a time, and putting the last two tiles of a row into place usually means temporarily breaking the row you just finished. Experienced solvers work from the top down, locking each row as they go. This version adds selectable difficulty levels and an auto-solve button, which exists mainly to prove a position is solvable if you start to suspect it is not. It always is: the shuffle never produces one of the unsolvable arrangements.
How to Play 15 Puzzle - Collect numbers
Click or tap a tile next to the empty square to slide it into the gap, or use the arrow keys. Only tiles directly beside the space can move, so plan a route for a tile rather than aiming it at its destination in one go. Choose a difficulty level before you start, and use the auto-build button if you want the game to finish a position for you.
Tips and Tricks
Solve the top row and the left column first, then treat what remains as a smaller three-by-three puzzle. Repeat until only a two-by-two corner is left.
To place the last two tiles of a row, park them in the corner in the wrong order and rotate them into place. Slotting them in one at a time will always push the other back out.
Steer the empty square rather than the tiles. Thinking of the gap as the thing you are moving makes long detours much easier to plan.
If the final four tiles will not resolve, a row above is almost certainly out by one. Unlock that row and redo it instead of shuffling the corner endlessly.
Frequently Asked Questions
Is every shuffle actually solvable?
Yes. Half of all possible arrangements of the 15 Puzzle cannot be solved at all, but this version only deals positions from the solvable half. A board that will not come out is a planning problem, not a dead end.
What is the auto-build button for?
It finishes the current position for you. It is most useful as a check - if you doubt a board can be completed, run it and see the solution rather than abandoning a puzzle that was fine.
Is there a time limit?
No. The puzzle waits as long as you need, which suits it: most of the work is thinking about the next few moves rather than making them quickly.
Do I need to install anything?
No. The 15 Puzzle runs in the browser on GN Math and works with a mouse, the arrow keys, or by tapping on a phone or tablet.
How many moves should it take?
A well-shuffled board can be solved in around eighty moves by someone who knows the row-by-row method. First attempts often run into several hundred, which is entirely normal.
Tags
sliding puzzle, 15 puzzle, number puzzle, brain game, logic puzzle, classic puzzle, single player, browser game, no download, tile game
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