Gomoku

Gomoku is the classic five-in-a-row game. Two players take turns placing stones on a 15×15 board, each trying to be the first to make an unbroken line of exactly five stones.

Rules

• There are two colours, black and white, and black places the first stone.
• Players take turns placing one stone of their colour on any empty point.
• Stones are never moved or removed once placed.
• Your colour can change during the opening (see below). Each stone keeps its colour for the whole game, and you own the stones of whichever colour you are playing.

Opening

Black has a strong advantage in five-in-a-row games, so Gomoku uses the swap2 opening to make the start fair:

1. The first player places three stones: black, then white, then black. They can go anywhere on the board.
2. The second player then chooses one of three options:

• Stay white and place the next white stone.
• Swap: take over black, so the first player now plays white and places the next stone.
• Swap2: place two more stones, one white and then one black, and leave the choice of colour to the first player.

After a swap2, the first player chooses to either stay white and place the next stone, or swap to black.

Normal play follows, one stone per turn. A good opening leaves your opponent with the game balanced - no colour is clearly in a better position.

Game End

• The game ends as soon as one player makes exactly a line of five. The line of five can be horizontal, vertical, or diagonal. An overline (6 or more in a row) is a legal move but wont win.
• If the board fills up and nobody has made exactly five in a row, the game is a draw.