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About this tool
Free 15 puzzle sliding number game online — solve 3x3, 4x4 and 5x5 boards in the fewest moves.
The Sliding Puzzle is the classic 15 puzzle: numbered tiles in a grid with one empty cell, which you slide into order with the blank finishing bottom-right. It offers 3x3, 4x4 and 5x5 boards, and every shuffle is run through the inversion-parity check and corrected if needed, so you are never dealt one of the arrangements that cannot be solved. Moves and time are counted, and your lowest move count for each board size is kept separately.
Open Sliding Puzzle on AltFTool — it loads instantly in your browser.
Add your input to the workspace.
Adjust the options until the result looks right.
Copy or download the output and put it to work.
Shuffles are checked with the standard inversion-parity rule and repaired if they fail it, so no attempt is wasted on an impossible board — and it never hands you an already-solved one.
Tapping any tile in the blank's row or column shifts the entire segment toward the gap, so a three-tile run takes one tap rather than three.
Arrow keys or WASD move the blank and Space starts and pauses, with the keys only captured while a game is actually running so the page still scrolls otherwise.
No — exactly half are. For an odd-width board the arrangement is solvable when the inversion count is even; for an even width like 4x4 it is solvable when inversions plus the blank's row counted from the bottom is odd. This puzzle applies that test to every shuffle and fixes any deal that fails it.
16! = 20,922,789,888,000 arrangements in total, of which exactly half — 10,461,394,944,000 — are reachable from the solved state. The 3x3 version has 9!/2 = 181,440 reachable positions.
The hardest possible 4x4 position needs 80 single-tile moves, a result established by exhaustive search; for the 3x3 board the worst case is 31 moves. A typical random deal takes far fewer, which is why the move counter is worth racing against.
Work top-down and left-to-right: finish the top row completely, then the next row, and once only two rows remain solve them column by column. The last two tiles of each row usually need a short three-move cycle to rotate them into place rather than being pushed in directly.