Chess960 (Fischer Random)
Play Chess960 against the computer, with proper Fischer Random castling — including the king that swaps places with its own rook.
Your record, level by level
Kept separately from the standard board, because they are different games — an opening repertoire is worth nothing here. Stored in this browser only. A draw counts half a point and holds a winning streak rather than ending it, and only games against the computer are recorded.
Moves
Castling is the whole difficulty
The king always finishes on g1 and the rook on f1, or the king on c1 and the rook on d1 — exactly where they land in ordinary chess. Everything strange follows from the fact that they start somewhere else. The king may travel one square, five squares, or none at all. It may move backwards: from b1, castling kingside sends it right across the board to g1, while castling queenside shifts it one square to c1. And it can finish on the square its own rook was standing on — a king on f1 with a rook on g1 castles by swapping places with it.
Your own rook can block you. Every square either piece crosses must be empty apart from those two pieces. With a back rank of rook, king, rook on a1–c1, castling queenside needs the king on c1 — where the other rook is sitting. That position simply cannot castle queenside until the kingside rook moves, and there is nothing like it in standard chess. Several of the 960 openings are one-sided for this reason.
- Position 518 is ordinary chess. The numbering is a standard scheme, so 518 always means the familiar back rank and everyone can reproduce a game from its number alone.
- The bishops always start on opposite colours and the king always starts between the two rooks. Those two rules are what cut the 40,320 arrangements of eight pieces down to exactly 960.
- Both sides get the same back rank, mirrored — so the position is symmetrical and neither player is handed an advantage by the shuffle.
- Opening theory is worth almost nothing, which is the point. Bobby Fischer proposed the variant in 1996 precisely to move the game away from memorisation and back to play from the first move.
- Undeveloped bishops can start on the corner, and a queen or knight can find itself in the corner too. Working out which pieces are badly placed is the first real problem of every game.
How to use
- Pick a position number, or hit Random for one of the 960.
- Choose a difficulty and which colour you want.
- Work out which pieces are badly placed before you move — that is the first real problem.
- Remember castling always finishes on g and f, or c and d, wherever the king started.
Frequently asked questions
What is Chess960?
Chess with the back rank shuffled. Bobby Fischer proposed it in 1996 to move the game away from memorised opening theory and back to play from the first move. Two rules constrain the shuffle: the bishops must start on opposite colours, and the king must start somewhere between the two rooks. Those two conditions cut the 40,320 possible arrangements down to exactly 960, which is where the name comes from.
How does castling work in Chess960?
The pieces always finish where they finish in ordinary chess — king on g and rook on f for the short castle, king on c and rook on d for the long one. Everything unusual follows from them starting somewhere else. The king may travel one square, five, or none at all, and it can move backwards: from b1, castling short sends it right across to g1 while castling long moves it one square to c1.
Can the king really land on its own rook’s square?
Yes, and it is the case that catches every engine written carelessly. A king on f1 with its rook on g1 castles short by swapping places with it — the king ends on g1 and the rook on f1. Both pieces have to be lifted before either is put down, because writing them in the obvious order erases one of them.
Why can some positions not castle one way?
Because every square either piece crosses has to be empty apart from those two pieces, and the other rook can be standing in the path. With a back rank of rook, king, rook on a1 to c1, castling long needs the king on c1 — which is exactly where the kingside rook is. That position cannot castle long at all until the rook moves, and there is no equivalent situation in standard chess.
Which position number is ordinary chess?
518. The numbering follows the standard scheme, so 518 always means the familiar back rank on any site that implements it, and any game can be reproduced from its number alone. It is worth playing once as a sanity check that everything behaves the way you expect before trying a shuffled one.
Do both players get the same back rank?
Yes, mirrored. The position is symmetrical, so neither side is handed an advantage by the shuffle — the only asymmetry is the usual one of moving first. This is also why a position that cannot castle one way cannot castle that way for either player.
Is opening theory any use?
Almost none, which is the point. Roughly one position in a thousand is the standard one, and the general principles still apply — develop, take the centre, get the king safe — but the specific move orders that make up opening preparation do not transfer. Most players find the first ten moves genuinely hard in a way standard chess stopped being for them years ago.
Are the records separate from the standard board?
Yes, because they are different games and a repertoire in one is worth nothing in the other. Both boards keep a record per difficulty level rather than one combined tally, since beating the gentle engine twenty times says nothing about the tough one. Everything is stored in your browser and never uploaded.
Why track wins per level rather than a single score?
Because a single number hides the thing you actually want to know — which level you have mastered and which one still beats you. A combined tally looks the same whether you are beating the hardest setting occasionally or the easiest one constantly. Each level keeps its own played, won, lost, drawn, fastest win and longest streak.
How is a draw counted?
As half a point, following the usual chess convention, and it holds a winning streak rather than ending it — a draw is not a loss. Only a loss resets the streak to zero. The percentage shown is the share of available points rather than the share of games won, which is how chess results are normally scored.
What counts as a fastest win?
The fewest plies, converted to moves for display. Plies count each side’s turn separately, which is the fair comparison, because winning as Black in twenty moves is a longer game than winning as White in twenty. Only games against the computer are recorded, since a two-player game has no difficulty to attribute the result to.
Is the engine strong?
No — it searches a few moves deep and evaluates material, position and king safety, which makes it a reasonable club-level sparring partner rather than a serious opponent. It runs entirely in your browser with nothing sent anywhere, which is the trade being made. In Chess960 it is on much the same footing as you are, since it has no opening book to fall back on either.
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