Mindcrew puzzle bench
15Square
About 15Square
15Square is a sliding tile puzzle built around the classic fifteen-puzzle idea: numbered tiles sit in a square grid with one empty space, and each move slides a tile into that gap. The familiar 4 x 4 version became widely known in the 1880s, and it still has a useful mathematical edge because not every random arrangement can be solved.
The app supports 3 x 3, 4 x 4, 5 x 5, and 6 x 6 boards. Smaller boards are good for short sessions and learning the pattern; larger boards reward planning because every solved row or column becomes a constraint you need to preserve while finishing the rest of the puzzle.
Behind the scenes, each fresh puzzle is generated from a solved board by making valid shuffling moves. That means the position is reachable before you start, rather than being a random tile order that might fail the parity test.
How to play
Choose a board size, start a new puzzle, then slide tiles toward the empty square until the numbers are back in order. On desktop you can use the arrow keys or click any tile in the same row or column as the gap. On phones and tablets, tap or swipe the board to move tiles quickly without needing tiny buttons.
For 3 x 3, solve the first row, then the left side, and finish the remaining cycle. For 4 x 4 and larger boards, work row by row from the top and column by column from the left, leaving the final two rows and columns until the end. The last section is usually a rotation problem, not a speed problem.
The Save and Load controls use local browser storage, so saved games stay on the device you are using. Undo steps back through recent moves in the current session, and Solve gives you a deterministic reference path when you want to study the structure rather than chase a score.
FAQ
Why are some sliding puzzles unsolvable?
A sliding puzzle has a parity rule based on tile inversions and, on even-width boards, the row containing the blank square. If a shuffled board has the wrong parity, no legal sequence of slides can solve it. 15Square avoids that by shuffling through legal moves from the solved state.
What is a good move count?
It depends heavily on board size and shuffle depth. A 3 x 3 puzzle can often be solved in a few dozen moves, while 5 x 5 and 6 x 6 boards are better treated as longer planning puzzles. The leaderboard is local, so compare against your own best scores on the same device.
Why does the Solve button not simply teleport the board?
The solver is intended as an explanation aid. Showing legal moves preserves the rules of the puzzle and makes it easier to see how rows, columns, and the final cycle are handled.
Does progress persist across browsers?
No. Saves, best scores, theme choice, and consent preference are kept in local browser storage. They do not sync to a Mindcrew account.