The objective
Win by checkmating the opposing king: the king is under attack and cannot move, block the attack or capture the attacking piece. A move that leaves your own king in check is not legal.
How the pieces move
Pawns move forward, knights jump in an L-shape, bishops travel diagonally, rooks move in straight lines, queens combine rook and bishop movement, and kings move one square in any direction.
Special moves
Castling
Castling moves the king two squares toward an eligible rook, then places that rook beside the king. It is only legal when the path is clear and the king does not start in, cross or land in check.
En passant
A pawn may capture an opposing pawn that has just advanced two squares, as if it had advanced only one. The capture must be made immediately on the next move.
Promotion
When a pawn reaches the last rank, choose a queen, rook, bishop or knight. Promotion can change the outcome of an endgame in one move.
Draws
Board Duel records stalemate as a draw. It also uses the 50-move rule when no pawn move or capture has happened for 50 moves by each side.