The game of Hex was invented and popularized in Denmark by Piet Hein in 1942, and later independently rediscovered by John Nash in 1947. The game is attractive because it has extremely simple rules, yet a surprising amount of strategic depth. Another interesting aspect is that the game can't end in a tie.
The board has two red edges and two blue edges. Each player's goal is to connect their two edges by stones of their color.
The players alternately place a stone of their own color on the board, with Red going first. A stone can be placed on any empty cell. Once placed, stones are never moved or removed.
The swap rule
To make sure the first player does not have an unfair advantage, the swap rule is used. After the first player opens with a red stone, the second player has the option to "swap", or steal the opponent's first move. In this case, Red's initial stone is replaced by a blue stone and mirrored about the long diagonal. After this, it is Red's turn.
The game ends when one of the players has connected their edges with a path of stones of their color. The game can't end in a tie. When it is clear to both players who will win, it is customary for the losing player to resign.
Game options and interface
The game can be played on boards of several different sizes. The 6x6 board is designed to help beginners understand the basic rules and discover simple game patterns. The 11x11 board is a more classic size and was used by Piet Hein. The 13x13 board is preferred by many experts. The 14x14 board was recommended by John Nash, and the 15x15 board allows even longer plays.
The 6x6 board size is only available in training mode.
Moves and swapping
To make a move, click on an empty cell. To guard against accidental misclicks, you have to confirm each move by clicking on the stone a second time (or use the "confirm" or "cancel" buttons above the play area).
On the second move of the game, you have the option to swap. To do so, click on the "swap" button above the play area. If you do not want to swap, simply make a normal move.
Players can resign at any time (whether or not it is their turn). The resign button is found in the "additional game controls" menu, which is marked by three dots "..." in the upper right corner of the play area.
Passing (i.e., skipping a move) is rarely done in Hex. The reason is that passing never benefits a player: if you can win by passing, you can also win by making a random move. Nevertheless, the ability to pass has been included in the Board Game Arena implementation of Hex. It has certain specialized uses, such as teaching, giving handicap (i.e., giving an advantage to the weaker player), or setting up an initial board position.
The option to pass is found in the "additional game controls" menu, which is marked by three dots "..." in the upper right corner of the play area. If your opponent passes and you do not want to allow it for some reason, simply pass yourself, which effectively returns the game to its previous state. Three passes in a row are not permitted, so if both players have passed, the next player must make a proper move.
The shades of red and blue that Hex uses by default can be difficult to distinguish for colorblind people. To compensate for this, there is now a "Color blindness" setting in the "Options" below the game board. It changes the colors to be more easily distinguishable. (Limitation: this currently only works for games in progress, and not during replay).