The ko rule
Surround territory, keep your groups alive, and count at the end.
Some positions let each player capture one stone back immediately, over and over, with the board returning to the same shape every two moves. The ko rule stops that: after your stone has been captured in a ko, you may not recapture immediately. You have to play elsewhere first, and only then come back. It is the one rule in Go that exists purely to make the game end.
What a ko looks like
A ko arises when a single stone captures a single stone and the resulting position would allow an immediate recapture that restores the previous board. Without a rule, the two players could repeat that forever.
The board here enforces the simple, single point version: the point just captured is forbidden for one turn. Play anywhere else and it opens again.
Ko fights, and why they are strategic
Because you have to play elsewhere before recapturing, that move is worth thinking about. A ko threat is a move somewhere else on the board big enough that your opponent must answer it. Answer it they do, and now you may retake the ko.
So a small one point ko turns into a contest about who has more big threats available elsewhere. Games have been decided by nothing else.
Beginner advice
On a small board, do not start a ko fight over something trivial while your opponent has three unanswered threats on the rest of the board. Count the threats before you start, in the same way you would count liberties before a capturing race.
Play a game
Reading about a game is practice for playing it and nothing more. The board is open, it is free, and nothing needs installing.
Common questions
- What is the ko rule in Go?
- You may not immediately recapture a stone in a ko, because that would repeat the position. You must play elsewhere first.
- What is a ko threat?
- A move played elsewhere that is big enough to force an answer, which buys you the chance to retake the ko next turn.
- Does the ko rule apply to bigger repeats?
- The board here uses the simple single point ko, which covers the situation nearly every game runs into. More elaborate repetition rules exist in tournament rulesets.
More on Go
Liberties and capture
A group of stones lives by its liberties, the empty points next to it. When the last one is filled, the group is captured. The one rule the rest of Go is built on.
Two eyes and life
A group with two separate eyes can never be captured. What an eye is, why one is not enough, and how to tell a real eye from a false one.
How Go is scored
How a game of Go actually ends and who wins. Area scoring explained, why White gets komi, and how to count without arguing.
Playing Go on 9x9
Small board, whole game, twenty minutes. Why 9x9 is the best place to start Go, what changes on it, and the opening principles that work.
This site is built around Xiangqi, Chinese chess. If you enjoy Go, the rules of Xiangqi take about five minutes, and there is always somebody to play.