Move the king two squares toward the rook.
Ensure the rook is on the same rank as the king (same row).
Use either king-side castling (king toward the kingside rook) or queen-side castling (king toward the queenside rook).
Confirm neither the king nor the chosen rook has moved previously.
Confirm the king is not currently in check.
Confirm all squares between the king and the rook are empty.
Confirm the king does not pass through or end on a square that is under attack by an opponent’s piece.
After castling, place the rook on the square the king crossed (the king ends two squares from its starting square).
Notation: King-side castling is written as “O-O”; queen-side castling is written as “O-O-O”.