THE RULEFifteen numbers. One empty seat.
Read the finished board like a page: 1–4 in the first row, then 5–8, 9–12, and 13–15 with the gap last. Each turn slides one tile horizontally or vertically into that gap. You cannot lift a tile out, jump over another, or swap two numbers.
GET YOUR HANDS ON ITTap a neighbor. Start a thought.
On a phone, tap any outlined tile beside the gap. With a keyboard, focus the board and press an arrow in the direction you want a numbered tile to travel. The timer waits for your first move. Pause whenever you need a break; your unfinished board follows you between these two pages in the same tab.
A SLIDING-PUZZLE HABITPlan the empty space, too.
A number can be one square from home but still have no way in. Before moving it closer, find a route for the empty space to get behind it. Try arranging 1 and 2 first, then treat 3 and 4 as a pair. Clearing a row together works better than chasing whichever tile looks easiest.
Practice the row-by-row approach →FIND YOUR STARTING POINTOne board, three kinds of challenge.
Easy begins just ten legal slides from the finish. Medium and Hard spread the tiles farther, asking you to leave room for bigger cycles. These shuffle lengths are not shortest-solution promises. The related 8 Puzzle uses a 3×3 board. Choose a size in the sliding puzzle collection; each full game has three difficulties and optional hints.
Need help seeing a route? Hint reveals one move at a time. Assisted bests have their own record, so your independent solves keep their place.