The double three — also called a three-three — is the second great winning pattern of gomoku after the four-three. With one move, you create two open threes at once. The defender can block only one; the other becomes an open four, and you win.
It is simple in principle, but it has one weakness the four-three does not, and understanding that weakness is what separates players who win with double threes from those who get punished for them.
How it works
A double three needs two of your lines, each with two marks and open space, crossing at an empty point. Playing at that point turns both twos into open threes at once.
In the diagram:
- X plays h8. Row 8 now has f8–g8–h8 with empty e8 and i8 (and d8, j8 beyond): an open three. Column h has h8–h9–h10 with empty h7 and h11: another open three.
- O blocks one — say, i8 on the row.
- X extends the other — h7 or h11 — to make an open four on column h.
- O blocks one end; X makes five at the other.
The weakness: fours
A double three does not force an immediate specific reply the way a four does. The defender is threatened with an open four next move, not with five. That gives the defender one move to do something — and if the defender has a four available, they can play it.
A defender's four must be answered. If the defender can make several fours in a row, each one forcing a reply, they may:
- place one of those four-marks on the attacker's three, blocking it with a forcing move, or
- reach a combination of their own and win first.
This is why the rule of thumb is: before playing a double three, check whether the opponent can make any fours. If they cannot, the double three wins. If they can, look more carefully — or prefer a four-three, which leaves them no time.
Building double threes
Double threes come from twos crossing at empty points. In the diagram, X's row two (f8–g8) and column two (h9–h10) crossed at h8. To create chances like this:
- Place your marks so that twos in different directions share an empty point.
- Use the gaps: split twos (X _ X) cross other lines at their gap as well as at their ends.
- Build more than one crossing. The defender can take away one crossing per move, but not two.
Quiet moves in the middle game are ideal for this. A move that adds a two on one line while pointing at an existing two on another line creates a new crossing. See twos and potential.
Defending against double threes
The defence has two layers:
- Before the double three: occupy crossing points where the attacker has two twos meeting. This is the most efficient defence.
- After the double three: block one three — ideally the one whose extension would be more dangerous — and look for any four of your own to regain the initiative. If you have none, the position is usually lost.
When choosing which three to block after a double three, prefer to block in a way that also cuts the attacker's other resources or builds a four for you.
Broken double threes
One or both of the threes in a double three can be broken — for example, one solid three and one X X _ X shape. These are even harder to see and just as effective. A defender blocking only the obvious solid three may not notice the broken three at all. Read broken threes.
The double three in renju
In renju, the professional variant, the first player is forbidden from making a double three. It is one of several restrictions designed to reduce the first player's large advantage. The second player may make double threes freely.
Neither freestyle gomoku nor Vietnamese caro has this restriction, so on this site both players may use double threes. But knowing about the renju rule is useful if you ever play in a renju club.
Double three under blocked ends
The pattern works under blocked-ends rules as well. When the surviving three becomes an open four and then a five, that five has at least one open end. The only caveat: check the far ends. If one of your threes already has an enemy mark just beyond its extension on one side, its "open four" may be closer to a closed four, and the combination may fail. Count before you commit.
Choosing between a double three and a four-three
Sometimes you have both options available: one move makes a double three, another makes a four-three. Prefer the four-three unless you have a clear reason not to. It is more forcing, it leaves the defender no time for counter-fours, and it is easier to calculate.
Choose the double three when the four-three would waste a valuable line — for example, when the four's forced block would land on a point that strengthens the defender's own attack. In that case, a double three that keeps your fours in reserve may be stronger, as long as the defender has no fours of their own.
A defender's view
If you are the defender facing a position where the attacker has two twos meeting at a crossing, remember that you do not have to wait. Placing your mark on the crossing point is a quiet move, but it removes the whole combination at once. Blocking one of the twos elsewhere is weaker, because the attacker may simply build a new two pointing at the same crossing.
Practice
On the home board, play a series of games whose goal is to win with a double three. Each time you play one, first check the computer's possible fours. If you win, replay the game from your account and find where your two twos first crossed. If you lose after playing a double three, find the four that the computer used to escape — that is the lesson.
Frequently asked questions
What is a double three in gomoku?
A single move that creates two open threes at once. The defender can block only one; the other becomes an open four.
Is a double three allowed in caro?
Yes. Vietnamese caro and freestyle gomoku have no restriction. Renju forbids it for the first player, and some other regional variants have their own restrictions, but not the rules used on this site.
Why did my double three fail?
Most likely the defender had fours available. Each four forced you to answer, and they used those moves to block your threes or build their own attack.
Which is stronger, double three or four-three?
The four-three is more forcing and more reliable. The double three is strong when the defender has no fours.
