As per the chess rules
, if the current position on the chess board appeared 3 or more times, the game can be declared a draw by either of the opponents. The other player's approval is not required, and the game ends immediately and is recorded as a draw for both players.
Please note that simply repeating the same move 3 or more times by one of the players might not be enough, as the entire position
on the board has to be repeated. That also includes whose turn it is to move, all castling possibilities and capture en passant targets.
It is not required that the same position occurs three times during the consecutive moves. However, it usually happens this way in practice, typically with one of the Kings being subjected to a perpetual check.
To declare the draw in a game due to the threefold repetition rule, please use "Declare draw" link located directly below the game board.
It is a perfectly valid strategy in chess to force the game to end in a draw, if otherwise the player is facing losing the game.