About this game
Fifteen plaques and one very useful hole
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A four-by-four tray, fifteen numbered plaques and a single empty socket. Nothing slides freely. The only legal destination on the whole tray is that one empty socket, which makes the hole itself the thing you are really operating rather than an absence in the middle of it. Learning this puzzle is mostly learning to think about the hole rather than the numbers.
It is the quietest thing on this site. No opponent, no timer running you down, no failure state at all — you cannot lose Fifteen, you can only still be doing it. The clock is there if you want something to race, and completely ignorable if you do not.
Where it comes from
The puzzle appeared in the 1870s, most likely from Noyes Chapman, a postmaster in New York State, and by 1880 it had become a genuine international mania — newspapers ran solutions, employers complained about it, and it was sold in every toy shop in Europe and America.
Its notoriety came from a lie. Sam Loyd, the puzzle showman, claimed to have invented it and offered a thousand-dollar prize for solving a board with the 14 and 15 swapped. The prize was safe: Johnson and Story had already shown in 1879 that exactly half of all arrangements are reachable and half are not, and Loyd's was in the wrong half. The money was never at risk, which is presumably why he offered it.
What this version does with it
The board here is dealt only from the solvable half, so no arrangement you are given is a trick. Beyond that, the work went into the object. The plaques are brushed brass with dark struck numerals and a hairline of gold inlay, seated in an aged-bronze tray whose inner well is deliberately dark — a fifteen puzzle needs the empty socket to read as a real hole, and metal on metal at one value loses it immediately.
Moves and time are both counted, because they measure different players. A careful solver wants a low move count; a practised one wants a low clock. Your board, your count and your clock all survive a closed tab, so this is a reasonable thing to leave half-finished. There is a haptic tick on each slide, which is one of the few places on the web where a small vibration genuinely improves a puzzle.
Thirty seconds to start
- Tap any plaque next to the gap and it slides in. Swipes and arrow keys work too.
- Tap a plaque further along a row or column and the whole run shifts together.
- The target is 1 to 15 reading left to right, top to bottom, with the gap finishing bottom-right.
Why it is worth learning properly
Shuffling hopefully will solve the top half and then strand you forever. The puzzle has a real method — finish the top row, then the second, then work the last two rows in vertical pairs, so that each solved region stays solved while you work below it. It takes about ten minutes to learn and it makes every board finishable, including the two positions that look impossible and are not. That method, corner tricks and all, is written out step by step in the guide.