Chess960, every one of them

Castling is the whole game, and it is the rule everyone gets wrong

Ordinary chess castling is described by how far the king travels: two squares, that way. That description is wrong in Chess960 and it is why people bounce off the game. The real rule is about where the pieces finish: the king ends on g1 and the rook on f1 for the short castle, the king on c1 and the rook on d1 for the long one — c8/d8 and g8/f8 for Black — whatever files they started on.

Four things follow that almost nobody expects, and every one of them is a legal move you can play on this board:

• The king may not move at all. King already on g1, rook on h1: castling short is the rook going h1 → f1 and the king standing still.
• The rook may not move at all. Some arrays put a rook on d1 or f1 to begin with.
• King and rook can swap squares. King f1, rook g1: after O-O they have traded places.
• The king can travel toward the h-file to castle long. King b1, rook a1: O-O-O sends the king b1 → c1 and jumps the rook over it to d1.

Two safety rules get confused as well, and they are not symmetrical. Every square from the king's start to the king's finish, inclusive of both, has to be free of enemy attack — so a king in check can never castle, even in the case where castling would not move it. The rook's path is only checked for being empty: a square that just the rook crosses may be attacked and the castle is still perfectly legal.

The rail panel names both castles for the array you are on — the one you can play and the one you cannot, with the reason — and the board draws both landing squares when you pick the king up. Because two different moves can put your king on the same square (with the king on b1 and rooks on a1/h1, the plain king move b1 → c1 and O-O-O both end with a king on c1, and they are different moves), this board gives them two different gestures rather than guessing. The rule is on the board and it has one exception-free form: a gold ring means tapping here castles, and nothing else on the board ever wears one. Your rook always carries one — that is the king takes rook gesture, and it always works. The king's landing square carries one only where no ordinary king move happens to reach it; where one does, tapping it makes that ordinary move, and the square shows the ordinary marker instead. That ambiguity is exactly why Chess960 engines write castling as king-takes-rook, and both moves are generated here and counted by the published perft the engine is checked against.

Pick your position — all 960 of them

Every legal Chess960 array has a number from 0 to 959 under Reinhard Scharnagl's standard numbering, which is what commentators mean by “SP-518” or “position 356”. Type one, roll one, or step through them; 518 is ordinary chess, and starting there is a fair way to prove to yourself that nothing else changed. The 🔗 button gives you a link that opens that exact position, so you and a friend can start the same board from two devices without agreeing on anything else first.

Why exactly 960? Two constraints do all the work: the bishops must sit on opposite-coloured squares, and the king must sit strictly between the two rooks. Of the 5,040 distinct arrangements of the eight back-rank pieces, exactly 960 survive both. Our test suite derives that by brute force from the constraints themselves and then matches the surviving set piece-for-piece against the numbering this page uses, so the number is checked against an independent derivation rather than against itself.

Fischer Random, Chess960, Freestyle Chess

One game, three names. Bobby Fischer announced it in Buenos Aires in 1996 as Fischer Random Chess; “Chess960” is the name that counts the positions and is what FIDE uses in Appendix F of its Laws of Chess; and Freestyle Chess is the branding of the Grand Slam tour that has carried the game since 2024, which is why the search term moved. The rules are identical under all three. What the shuffle removes is opening preparation: on position 356 nobody has a book line, so you are thinking from move one instead of move fifteen.

Where our engine's limits are, stated plainly

The move generator here is the same one behind our ordinary chess board, which is checked against published perft counts; the Chess960 layer on top of it adds the 960 arrays, the castling rule and the Shredder-FEN castling field, and nothing else. It is verified against the published 960-position Chess960 perft suite, taken from two mirrors that were diffed against each other before a number was used.

The honest caveat: that published suite gives node counts for positions eight plies into a game, not for the 960 initial arrays, and we could not find a published perft table for the initial arrays anywhere. So the starting positions are anchored two other ways instead — position 518 carries the standard published chess perft exactly, and the 18 arrays that put the king on e1 with rooks on a1 and h1 are positions where Chess960 castling and ordinary castling are literally the same rule, so both engines are run head to head on all 18 and must agree node for node. That is a real check and we would rather describe it than let “perft-verified” be read as more than it is.

The bot is a club opponent, not an engine. Three levels, alpha-beta with capture extensions and a material-plus-position evaluation. Hard will punish a hanging piece and find a short tactic; it will not out-calculate you in a sharp middlegame the way Stockfish would. There is no Chess960 opening book anywhere in it, which is arguably the fairest thing about it.

What this page does not have, said plainly

There is no clock. Both of the big Chess960 sites play timed games and we do not, in any mode — not against the bots and not in a friend room. That is a real gap rather than a design position: a lot of the people searching for a Chess960 board want a 3+0 blitz game, and this is not one. It is the first thing we would add.

There is no rating and no pool of strangers waiting. Quick Match pairs you with whoever happens to be here, and if nobody is, three computer levels are. lichess had over thirty-six thousand games in play on the day we measured them; we are not that and will not pretend to be. What this page is for is learning the game and playing a friend, and it is built for exactly that.

And we are not the only board with a position picker — lichess's analysis tool has one too, and prints the start position number beside it. What is different here is that the number and the array are on the board you actually play on, next to the castling the array implies, rather than in a tool you go to afterwards.

Play a friend on the same position

Create a room, send the four-letter code, and your friend joins from any browser on any device — resign and rematch included, and the rematch re-rolls the position so the second game is a new one. Quick Match pairs you with whoever is waiting. Both players always get the same array, mirrored, which is the rule that keeps Chess960 a fair game rather than a lottery.

Chess960 is a public-domain game. This implementation, its artwork and its engine are original to EveryGameMade. More free classics: chess · data-backed strategy guides · the whole arcade.