One large 12×9 board for a full game plus two small 6×5 boards for quick ones, with the rules and the chain strategy printed underneath.
Two players take turns drawing a single horizontal or vertical line between two adjacent dots. Complete the fourth side of a box and you claim it, write your initial inside, and take another turn immediately. When every line has been drawn, the player with more boxes wins.
Because completing a box grants another move, a single opening can cascade — one box leads to the next, and a long corridor of boxes falls in one turn. That turns an apparently gentle game into something genuinely tactical.
The game's real strategy is about chains — connected runs of boxes that all fall together. The player forced to open the first chain generally loses it, so good play is about controlling who runs out of safe moves first.
Strong players use the double-cross: rather than taking every box in a chain, you take all but the last two and then deliberately give those two away, which forces your opponent to open the next chain for you. Giving up two boxes to win a chain of eight is a good trade.
Before making a move that opens a chain, count how many boxes it contains and how many chains remain. If a game comes down to two chains, the player who must open the first one usually loses — the whole endgame is manoeuvring to avoid that.