I’ve just started learning the beautiful game of go and can recommend it to anyone. As explored by Joe Politz, the game ending and scoring rules can be complicated. The manuals I found online were not very clarifying for the purpose of playing my first games. So here is an overview of a simple ruleset you can start with.
The goban (go board) has 7×7, 9×9, 13×13 or 19×19 crossings on which you play. The crossings on the edges are included. Some crossings have star points (small dots) which you may ignore.
+-------------------+
| + + + + + + + + + |
| + + + + + + + + + |
| + + * + + + * + + |
| + + + + + + + + + |
| + + + + * + + + + |
| + + + + + + + + + |
| + + * + + + * + + |
| + + + + + + + + + |
| + + + + + + + + + |
+-------------------+
One player has black stones, the other white. Players never run out of stones.
A group is a set of one or more stones of the same colour that are horizontally or vertically adjacent. The following example contains 2 black groups and 1 white one:
+ + + + + +
+ b + w + +
+ + b w + +
+ b b w w +
+ + + w + +
+ + + + + +
The liberties of a group are the empty crossings that are horizontally or vertically adjacent to a stone of that group. This black group has 2 liberties:
+ + + +
+ w o +
w b b o
-------
For the sake of simplicity, a player’s territory consists of the empty groups that are adjacent only to this player’s stones. So these are black’s territories of size 2 and 5:
+ b b +
b o o b
+ b b +
+ + b |
+ b o |
+ b o |
b b o |
b o o |
------+
and neither player has territory (yet) in these weird examples:
+-----------+
| + + + + b |
| + w w + b |
| w + + + b |
| + w w + b |
| + + + + b |
+-----------+
+-----------+
| + + + + + |
| + b b + + |
| b + w b + |
| + b b + + |
| + + + + + |
+-----------+
Players take alternate turns and black begins. Each turn, either pass (doing nothing) or place a stone on an empty crossing. When placing a stone, comply to:
The capture rule: when you occupy an enemy group’s last liberty, remove that enemy group from the board. You may not occupy the last liberty of one of your own groups, or create a new group with no liberties, unless that move provides that group new liberties. This is a valid sequence with 2 captures:
+ + b b |
b w w w |
b w + b |
--------+
+ + b b |
b w w w |
b w w + |
--------+
+ b b b |
b w w w |
b w w + |
--------+
+ b b b |
b + + + |
b + + b |
--------+
The ko rule: a move may not repeat a previous board position. This rule prevents black from capturing the white stone after the following sequence:
+---------------+
| + + + + + + + |
| + + + + + + + |
| + + + + + + + |
| + + + w b + + |
| + + w b + b + |
| + + + w b + + |
| + + + + + + + |
+---------------+
+---------------+
| + + + + + + + |
| + + + + + + + |
| + + + + + + + |
| + + + w b + + |
| + + w o w b + |
| + + + w b + + |
| + + + + + + + |
+---------------+
In the next turn, black may play anywhere except at the marked crossing. Once the board has a different position in a subsequent turn, the marked crossing may be available as a legal move:
+---------------+
| + + + + + + + |
| + b w + + + + |
| + + + + + + + |
| + + + w b + + |
| + + w + w b + |
| + + + w b + + |
| + + + + + + + |
+---------------+
+---------------+
| + + + + + + + |
| + b w + + + + |
| + + + + + + + |
| + + + w b + + |
| + + w b + b + |
| + + + w b + + |
| + + + + + + + |
+---------------+
A player who cannot make a valid move according to these rules, passes by default.
The game ends when either player resigns or when both players pass subsequently.
The player with the highest score wins. Your score is:
Generally, white receives 6½ komi points to compensate for not starting first.
In the following example with marked territories, black has 3 + 14 + 0 = 17 points and white has 3 + 23 + 6½ = 32½ points. So white wins by 32½ − 17 = 15½ points:
+---------------+
| + w o w b o o |
| b b w w b b b |
| w w w w w + b |
| w o w o w w w |
| w w w w w w b |
| b b b b w b o |
| + + w + w + b |
+---------------+
This is a simple version of area scoring. Once you start recognising (and mutually agreeing upon) ’dead’ groups that can inevitably be captured, you may use a more elaborate definition of ‘territory’ and end games earlier. See Sensei’s Library for alternative scoring systems. When you use a more established ruleset, you may use the exact difference in points to select handicaps or determine your rank. With the simplified rules, the exact score difference has less meaning.
For practice and offline multiplayer I like Little Go (iOS) and Goban 3 (OS X). CGoban (Java) seems ugly but nice for online play. I’m currently enjoying the book Go! More than a game by Peter Shotwell and Sensei’s Library is very informative. It’s tempting to write scripts for visualising goban positions; mine is aji.js.