Go variants

The difficulty in defining the rules of Go has led to the creation of many subtly different rulesets. They vary in areas like scoring method, ko, suicide, handicap placement, and how neutral points are dealt with at the end. These differences are usually small enough to maintain the character and strategy of the game, and are typically not considered variants. Different rulesets are explained in Rules of Go.

In some of the examples below, the effects of rule differences on actual play are minor, but the tactical consequences are substantial.

In Miai-Go, each player plays two moves at once, and their opponent decides which of the two should stay on the board.

All known forced Go cycles are impossible with this rule. The nature of the rule itself suggests that forced cycles are either impossible or astronomically rarer than they are in Go when the superko rule is not used.

Ko fights proceed in a similar manner to those of Go, with the difference that captures and moves answered by captures aren't valid ko threats. Although snapbacks are not possible in the basic variant (as it is necessary to make a ko threat before any consecutive capture occurs), they can be explicitly allowed with an extra rule while retaining the property that all known forced cycles are impossible.

The first player forced to capture one or more stones or to make a suicide move loses. Players try forcing their opponent into a losing move by building territory only they can play on.

In this variant, black is given a large handicap, and must prevent white from forming a stable group.

In this variant, intersections at the opposite sides of the board are considered adjacent, like on a torus. Therefore the playing board has no corners or sides and standard opening strategies that focus on capturing those parts of the board do not apply.

In Coin Go, a stone cannot be played on certain intersections of the board by either player. A coin may be placed on these intersections as a visual aid. Stones adjacent to a coin do not have a liberty at the coin.

There are different ways to determine intersections occupied by coins:

Coins may not be captured through liberty shortage. For scoring, coins do not contribute to territory. Normal scoring rules apply.

Variants for more than two players, but not altering the mechanism of the game

The international popularization of Pair Go has made big strides. In 2008, the World Pair Go Association (WPGA) was founded with the aim of further popularizing and developing Pair Go. As of September 2020, the association had 75 countries and territories affiliated with it. Matsuura Koichiro, the 8th Director General of UNESCO, serves as president. Also, the Committee to Make Pair Go an Olympic Sport was launched on June 30, 2015. In October 2019, the Japan Go Federation, an incorporated foundation, was founded by the Japan Pair Go Association in cooperation with the Nihon Ki-in and the Kansai Ki-in; it is the only body that represents the Japanese Go world internationally. It also is carrying out activity to secure the adoption of Go and Pair Go as Olympic sports in the future.

The two players use stones of the same color. This variation is regarded as a useful tool for developing one's memory and reading skills by forcing both players to remember who placed each stone. An external program or a third person may be used to keep track of who captures what in case one or both players forget the true color of a stone.

These variants are not purely strategic games, as the element of luck is quite important.

This game requires two players, a referee and three playing sets. Each player sees only his own board, while the referee can see them both and also has his own set. This variant is usually played on a 9×9 board. Players place stones on their boards, with no knowledge of what other players are doing. A referee keeps track of the game on the central board. If any player makes an illegal move, the referee informs him about it (some play that the referee says only that the move is illegal, while some, that the player is told whether the intersection is occupied or there is illegal ko capture). The player is allowed to make another move.

Although Go is most commonly played on a board with 19×19 lines, 9×9 and 13×13 boards are also available. They are used by beginners and by players who want a game that finishes more quickly. Due to flexibility of configuration, the two smaller sizes are more often played on the online Go servers such as KGS Go Server, and board sizes from 2×2 to 38×38 are also allowed.