How to play

The goal

The picture is cut into tiles and one tile is removed, which leaves a gap. The tiles are then shuffled. Your job is to slide them back until the picture is whole again.

How to move

You cannot pick a tile up. A tile can only slide sideways into the gap, which means only the tiles next to the gap can move at all.

• On a phone, tap a tile next to the gap, or swipe in the direction you want to push.
• On a computer, use the arrow keys. The arrow says which way you push a tile, so the gap travels the other way.

Sizes

Easy is a three by three board with eight tiles. Medium is four by four with fifteen tiles, and that is the classic version the puzzle is named after. Hard is five by five with twenty four tiles, which is a different experience entirely: it is less about seeing the picture and more about keeping your patience.

The buttons

• Peek shows you the finished picture. There is no shame in it.
• Numbers puts a number on every tile. If a picture is too subtle to read, numbers turn it back into a solvable puzzle.
• Sound adds a soft click for each move and a chime when you finish.
• New game reshuffles. Give up puts the picture back together for you.
• Challenge a friend copies a link. Whoever opens it gets the same picture and the exact same shuffle, so the comparison is fair.

Every shuffle can be solved

This matters more than it sounds. If you shuffle a sliding puzzle by randomly rearranging the tiles, half of the results are impossible to solve, and the player has no way of knowing which half they got. Here the board is shuffled by making legal moves backwards from the finished picture, so a solution always exists. If you are stuck, you are stuck, not cheated.

Three tricks that help

• Work top down. Finish the top row completely, then leave it alone and treat the rest as a smaller puzzle. Then the next row, and so on.
• Do the last two of a row together. The final corner of a row cannot be placed on its own without breaking what you just did. Bring both of the last two tiles near their place, then rotate them in as a pair.
• Watch the gap, not the tile. Experienced players think about where the gap needs to travel, because the gap is the only thing you actually control.

The clock

The timer starts on your first move, not when the page loads, so you can look at the picture as long as you like before you begin. There is no leaderboard and no account. The only person your time is measured against is you, and whoever you send the challenge link to.