Moves should be sent in syntax StartposEndpos, ex a2a4. Send "reset" through the input box to reset the game. If you make an invalid move, the game will simply ignore it-- it won't skip your turn or display an alert or anything. You can tell when someone has made a move by the fact that the page flickers as it updates. Converting of pawns and endgame detection are not currently supported, the game will simply stop when someone wins. The Repl backend for this can be found here.