Sliding Puzzle

The 15 puzzle has been frustrating and delighting people since the 1870s, and it still fits in the palm of your hand: a four-by-four grid holding fifteen numbered tiles and one empty square. Slide the tiles into that gap one at a time — by tap, click, or arrow key — until they run 1 through 15 in order with the space resting in the bottom-right. Every board here is shuffled from a solved state, so it is always genuinely solvable; the real contest is doing it in as few moves as you can. The method that untangles it is to work in shrinking chunks: lock the top row, then the left column, and keep peeling the puzzle down to a smaller and smaller square until only the bottom two rows remain, which you then finish two columns at a time. The awkward part beginners hate — setting up the last two tiles of a row as a pair before rotating them in together — is exactly the move that stops you undoing your own progress. Free in the browser, best-move count saved between games.