Gomoku pattern guide
Open threes, open fours and double threats
Quick answer: an open four is normally decisive because either end can complete five. Strong attacks aim to create two threats with one stone so a single defensive move cannot stop both.
What an open three means
An open three is a group of three stones with enough empty space to develop into an open four. It may be three consecutive stones or a shape with one internal gap, depending on the surrounding intersections.
Not every line of three is equally dangerous. A blocked end, the board edge or a cramped surrounding area can reduce the number of useful continuations.
Why an open four is usually decisive
An open four has four consecutive stones and an empty intersection at both ends. Blocking one end still leaves the other end available for five.
The defensive goal is therefore to stop the pattern before it reaches this stage. If the opponent already has a true open four and you do not have an immediate win of your own, one blocking move is not enough.
Closed fours still demand a response
A closed four has only one winning end because the other end is blocked by the edge or an opposing stone. Unlike an open four, it can be stopped with one move, but that response is urgent.
Do not continue a slow attack while the opponent has a one-move win.
Create two threats with one stone
A double threat is a move that creates two separate winning continuations, such as two strong threes or a four plus another line. The defender can cover only one point.
- Look for intersections shared by horizontal and diagonal lines.
- Use central stones because they participate in more directions.
- Avoid extending one obvious line repeatedly when every move can be blocked.
A simple defensive priority
- Take your own immediate five if one exists.
- Block the opponent's immediate winning point.
- Prevent an open four before extending a non-forcing attack.
- Break the intersection of a potential double threat.
- Only then return to building your own shape.