The Cờ Tướng Khó Nhất - Cờ Tướng O is an offline version of the online game. The game is played on a fixed board with 64 squares arranged in an 8×8 grid. Each player has 16 pieces: one king, one queen, two rooks, two knights, two bishops, and eight pawns. The objective is to checkmate the opponent's king by placing it under an escapable threat of capture.

The game begins with the player to the left of the king and the first move is made with the first piece, and the rest of the pieces are placed on the board according to the standard rules of chess. The game moves according to the standard rules of chess with two differences:

The pieces move according to the standard rules of chess, except that a piece can move to any empty space on the board.