Tile Slide

How to play

Put the tiles in order, left to right and top to bottom, with the empty space finishing in the bottom-right corner.

Tap or click a tile next to the space to slide it in. The arrow keys and W A S D slide a tile in that direction, and the pad below the board does the same — all three are the same move.

U takes a move back and R puts it forward. H asks for a hint, which marks one tile to move next.

Rules and controls

• There is one empty space, and it starts wherever it starts.
• Only a tile directly beside the space can move, and it moves into the space. There is no row push.
• The puzzle is finished when the tiles are in order with the space in the bottom-right corner.
• Finishing is decided by which tile is where — never by what the picture looks like.
• Moves and time are both counted from your first move.
• Every board can be solved. They are built by walking away from a finished one, so the way back always exists.
• A puzzle finished with hints still counts, but it will not take a best time from a run that used fewer.

Modes

• Classic 3 × 3 — Eight tiles and a gap. Small enough that a hint can prove it is showing you the best move there is.
• Standard 4 × 4 — Fifteen tiles. Hints find a way home rather than the shortest one — nothing can be quick and honest at this size.
• Grand 5 × 5 — Twenty-four tiles, and a long way round. For when you want to settle in.
• Daily Art — One picture a day, the same for everybody, built from the date. No undo — the run is the run.
• Use My Image — Your own picture, cut into tiles. It is read in this browser and never sent anywhere.

Tips

• Finish the top row and the left column first, then forget about them. What is left is a smaller puzzle of exactly the same kind, which is how the game's own solver works on the bigger boards.
• The last two tiles of a row will not go in one at a time. Put the second-to-last one where the last one belongs, bring the last one underneath it, and turn the pair in together.
• Watch the tiles-home count rather than the clock. It is the only number that tells you whether the last twenty moves achieved anything.
• On a photograph, turn the numbers on. Pictures have areas that look the same, and there is no prize for solving it the hard way.
• If you are stuck, take one hint rather than restarting. It costs you the best time and nothing else, and it always points somewhere that works from exactly where you are.

Privacy and local play

Everything runs in your browser. Your current puzzle, your settings, your best times and any picture you choose are kept on this device only — a picture is never uploaded, because there is nowhere on this site to upload one to. The button under the board clears all of it without touching any other Zerdly tool. No account, no sign-in, and nothing about your play leaves the machine you are on.

Questions

Can every puzzle actually be solved?

Yes, and it is guaranteed by how they are made rather than checked afterwards. Each board starts solved and is walked away from it by legal moves, so the moves that built it can always be run backwards. That matters more than it sounds: half of all the ways you could arrange the tiles cannot be solved at all, and there is nothing to see — it looks like an ordinary board until you are down to two tiles that will not swap.

Why not just shuffle the tiles?

Because a shuffle gives an unsolvable board about half the time. Walking away from the finished position avoids the problem entirely instead of testing for it. The walk also never immediately doubles back, which is not fussiness — over four thousand trials of sixty random moves, eleven boards came back completely solved and the typical board was only fourteen moves from finished. Refusing to undo the last move took that to zero solved and a typical twenty-two.

Does a hint show me the best move?

On the 3×3, yes, and it is proved rather than estimated — that board is small enough to search exhaustively, so the tile it marks is on a genuinely shortest route from exactly where you are. On the 4×4 and 5×5 it shows a move that definitely leads home but not necessarily the quickest one. Proving the shortest route on a 4×4 answered only seven of thirty boards within four million search steps, and a hint that made you wait for that — or that claimed to be best without checking — would be worse than an honest one. The game tells you which kind of hint you are getting each time.

How does the game decide the puzzle is finished?

By which tile is in which place, never by what the board looks like. That distinction matters most with your own photograph: a picture with a plain sky has tiles that are pixel-for-pixel identical, and a check based on the image would call the puzzle finished with two of them swapped. Tiles in order with the space in the bottom-right corner is the only thing that counts.

Why does every tile have a different shape on it?

So you can tell them apart without relying on colour. The artwork gives each tile a shape and orientation that nothing else on the board has, which stays true in greyscale and with any kind of colour vision deficiency. It takes some care: a rotated circle is still the same circle, so only rotations that genuinely change a shape are counted as different.

What happens to a picture I choose?

It is read in your browser, cropped to a centred square, scaled down and kept on your device. It is never uploaded, because there is nowhere on this site to upload it to — there is no account, no server that takes files, and no code in the game that can send one. The button under the board removes it from your device again.

Why can I not undo in the Daily?

Because everyone gets the same picture that day and you get one run at it, which is what makes the result worth keeping. Every other mode has undo and redo. The day rolls over at midnight UTC rather than your local midnight, so it changes at the same moment for everybody.

Can I move a whole row at once?

No. Only a tile beside the empty space can move, and it moves into the space. Tapping a tile further along the row does nothing except tell you so — this is the classic rule rather than the row-push variation, and the whole game is measured against it.

Does turning down the effects make it easier?

No. It removes the sliding animation and nothing else. The rules, the move count and the clock are identical either way, and the animation was never authoritative — the board commits the move immediately and the tile is then eased to where it already is.

Is anything sent to a server?

No. The puzzles, the solver, the hints, the sounds, your picture and your progress all run in your browser. There is no account, and clearing this game's data leaves every other Zerdly tool untouched.

Related interactives

• Traffic Escape — sliding pieces on a crowded grid, with a way out to find.
• Box Push — push crates onto their marks, where a move cannot be taken back.
• Slitherlink — draw a single loop that satisfies every clue.
• Bridges — join the islands so every one is reachable.