Castling consists of moving the king two squares towards a rook, then placing the rook on the other side of the king, adjacent to it. Castling is only permissible if all of the following conditions hold:

  • The king and rook involved in castling must not have previously moved;
  • There must be no pieces between the king and the rook;
  • The king may not currently be in check, nor may the king pass through or end up in a square that is under attack by an enemy piece (though the rook is permitted to be under attack and to pass over an attacked square);
  • The king and the rook must be on the same rank

Castling king's side

Castling king’s side with a fianchettoed bishop is very popular with many players. Diagram (a) shows that typical structure which is fine for chess but is a very closed position in CHEX because the g3 pawn is in the white bishop’s diagonal and is effectively blocking it in. Diagram (b) shows how this position could be set up in CHEX with the white bishop commanding it’s usual long diagonal and the f pawn still protecting the king. Alternatives are shown in diagrams (c) and (d).