Chess960, also known as Fischer Random Chess, is a variant of chess invented and advocated by former world chess champion Bobby Fischer beginning in 1996.

It employs the same board and pieces as standard chess, but the starting position of the pieces on the players' home ranks is randomized, under certain constraints. 

The random setup renders the prospect of obtaining an advantage through the memorization of opening lines impracticable, compelling players to rely instead on their talent and creativity.

Randomized Back Rank

Each player’s back rank (first row) is randomized according to the Chess960 rules:

1. Pawns remain on the second rank as usual.

2. The bishops must be placed on opposite-colored squares.

3. The king must be placed between the two rooks.

4. Both players use identical mirrored back rank positions.

Castling In Chess960

Each player is allowed to castle once if the following requirements are met:

1. It is the first movement of the king and the rook.

2. No square the king has to pass to its final position is under attack by opponent pieces.

3. All squares between the king and the rook's initial and final squares are vacant.

If castling is allowed and a player decided to do it, the final positions of the king and the rook are the same as the ones reached during castling in a standard game.

What is Chess960?

Chess960 is a variant of chess that employs the same board and pieces as standard chess, but the starting position of the pieces on the players' home ranks is randomized under certain constraints.

There are exactly 960 unique starting positions in Chess960!

Back Rank Constraints

Each player’s back rank (first row) is randomized according to the Chess960 rules:

• Pawns remain on the second rank as usual.

• Each player has one white squared bishop and one black squared bishop.

• The king must be placed between the two rooks.

• Both players use identical mirrored back rank positions.

Many players like to use a Chess960 random position generator.

Castling:
Each player is allowed to castle once if the following requirements are met:

• It is the first movement of the king and the rook.

• No square the king has to pass to its final position is under attack (or check) by opponent pieces.

• All squares between the king and the rook's initial and final squares are vacant.

• If castling is allowed and a player decided to do it, the final positions of the king and the rook are the same as the ones reached during castling in a standard game.

All positions will allow both kingside & queenside castling, but beware - some will positions will require you to move a rook before castling!

Fun Facts:
Did you know that Chess960 was invented and advocated by former world chess champion Bobby Fischer? 

It is also known as “Fischer Random Chess” and is the only chess variant recognized by the World Chess Federation (FIDE).