Gomoku Tactics: Open Threes, Fours and Double Threats

Gomoku tactics are about threats: shapes that will become five unless your opponent answers them. Every threat is defined by what it becomes in one more move, and almost every game is won by a move that creates two threats at once.

This guide names each shape, shows it on a diagram, and explains how to attack with it and defend against it. For the principles that decide which shapes to aim for, read the Gomoku strategy guide alongside it. X and O are the two players; a gold dot marks the key point, and letters mark points discussed in the text. Each diagram is a section of a larger board unless a thick line shows the edge.

The threat hierarchy

Shapes are ranked by how urgently they must be answered.

Shape	What it threatens next move	Must the opponent answer?
Open four	Five, in two different places	Cannot be stopped
Four (closed or broken)	Five, in one place	Yes, immediately
Open three (straight or broken)	An open four	Yes, usually this turn
Closed three	A closed four	No, but watch it
Open two	An open three	No

Two consequences follow. First, a four always comes before a three: if your opponent has an open three and you can make a four, your four must be answered first. Second, everything below "open three" is about preparation, not threats.

Open two

Two stones on a line with plenty of space on both sides.

An open two is not a threat, but it is a building block. A stone that creates two open twos in different directions is a strong quiet move, because it prepares two threes at once — exactly the kind of shape the opening guide aims to build.

Open three

Three stones in a line that can become an open four with one more stone.

The open three is the first real threat. If it is ignored, the next move makes an open four, which cannot be stopped. The space beyond the ends matters: if both sides have only one empty point before an opposing stone or the edge (O · X X X · O), the shape can only become a closed four, so it is not a real open three.

Broken three

Three stones with one gap, which still becomes an open four when the gap is filled.

Broken threes are easy to overlook because they do not look like a line yet. Treat them exactly like open threes.

Closed three

Three stones blocked on one side.

A closed three does not need an answer by itself. It matters as a resource: it can become a four at any moment, and a four forces a reply. Attackers use closed threes to gain tempo in the middle of a combination.

Open four

Four stones in a row with both ends open.

An open four is a win unless your opponent can make five first. The whole point of the open three is that it threatens this shape.

Closed and broken fours

A four with only one completion point. It forces an immediate block, but it can be stopped.

Fours are the strongest forcing moves in the game. A chain of fours that ends in a five or an open four is called a VCF (victory by continuous fours). Because each four has only one answer, these sequences are short to calculate — and they win even if your opponent has open threes on the board.

Double three

One move that creates two open threes at the same time.

A double three wins only if the opponent has no forcing move of their own. If they can answer with a four — or block one three with a stone that makes a four — they gain a tempo and may escape. In Renju, a double three is a forbidden move for Black; under freestyle rules and on 5Row it is allowed for both players. The Gomoku vs Renju comparison explains why.

Four-three

One move that creates a four and an open three.

The four-three is the most reliable winning combination, because the four leaves your opponent no choice: they must block it, and that block usually does nothing against the three. It is legal for both players in every common rule set, including Renju, where it is Black's main way to win.

Double four

One move that creates two separate fours.

A double four wins outright under freestyle rules. Two fours can also share one line — for example X · X X X · X, where either gap completes five — but those are rare in real games. In Renju, the double four is forbidden for Black.

Spotting threats

Most missed threats are missed for one of three reasons: they are diagonal, they are broken, or they come from a stone that was played for a different reason. A routine that catches them:

1. After every opponent move, check the four lines through that stone: row, column, both diagonals.
2. On each line, count the opponent's stones within five points of the new stone, including gaps.
3. Ask whether one more stone on that line would make a four, or an open four.
4. Then do the same for your own last move — your opponent may have left something of yours unanswered.

Defending against threats

Against a four: there is exactly one point. Play it, unless you can make five yourself.

Against an open three: you have several candidate points — both ends, and for a broken three, the gap. Choose by asking which block leaves the attacker the least.

Prefer blocks that also build your own lines. And before defending at all, check whether you have a four: answering a three with a four forces your opponent to respond first, and sometimes the sequence of your fours ends in a win.

Against a double threat: you are usually too late. The defence happened one or two moves earlier, when the point both lines shared was still empty. The how to win at Gomoku guide covers how to spot those points in time.

How the two-end rule changes tactics on 5Row

On 5Row the two-end rule is on by default: an exact five blocked at both ends does not win, and six or more always wins. That changes which shapes count as threats.

The general rule: under the two-end rule, a line boxed in between two opposing stones needs at least six free points to produce a winning five. A stretch of exactly five between them is dead, even though it would be playable under freestyle rules. The board edge is not a blocking stone on 5Row, so a stretch that runs to the edge only needs five. Two practical effects:

• Defending gets easier. A stone placed just beyond a closed four's completion point can neutralise it in advance.
• Overlines become weapons. If filling a point makes six in a row, it wins regardless of the ends. Watch for X X X X · X shapes.

The Gomoku rules page shows each two-end case with diagrams.

Tactical checklist

Before every move:

1. Can I make five? Can my opponent?
2. Does my opponent have a four or an open three, including broken and diagonal ones?
3. Can I make a four that leads somewhere — another four, a four-three, or an open four?
4. Is there an empty point shared by two of my lines? By two of theirs?
5. If I block, which point blocks and builds at the same time?

The fastest way to make this automatic is repetition: play a few practice games against the computer and name every three and four you see, yours and your opponent's.

FAQ

What is the difference between an open three and a closed three?

An open three can become an open four, which cannot be stopped, so it must be answered. A closed three is blocked on one side and can only become a closed four, which can be blocked with one move.

Which is stronger, a double three or a four-three?

The four-three. The four forces an immediate, specific reply, so your opponent cannot use their move to make a counter-threat. A double three gives them one free move, which is enough if they have a four.

Is a broken three really as dangerous as a straight three?

Yes. Filling its gap makes an open four, exactly like extending a straight three. It is just harder to see.

What does VCF mean?

Victory by continuous fours: a winning sequence in which every one of your moves is a four, so your opponent's replies are all forced.

Can I make a double three on 5Row?

Yes. 5Row has no forbidden moves for either player. Double threes are only forbidden for Black in Renju.