Once X has played the centre, O's first decision shapes the whole opening. There are essentially two families of answer: place your mark directly beside X's mark, or place it diagonally next to it. In the language of renju, these are called direct and indirect openings.
This article explains the two families, why they matter, and how the next few moves typically develop from each — without asking you to memorise anything.
The two families
After X plays h8, O's closest possible replies are the eight points surrounding it:
- Direct (orthogonally adjacent): h9, h7, g8, i8.
- Indirect (diagonally adjacent): g9, i9, g7, i7.
By symmetry, all four direct replies are equivalent, and all four indirect replies are equivalent. So there are really only two distinct choices.
O can also play further away — two points from X's mark, for example — but those replies give X more freedom and are much less common.
How renju uses these names
In renju, the professional variant of gomoku, the opening is standardised: the first stone goes in the centre, the second is placed directly or indirectly adjacent, and the third stone's position defines a named opening. There are 26 standard renju openings, 13 direct and 13 indirect, each with a traditional name. Serious renju players study them in depth.
You do not need any of that for freestyle gomoku or Vietnamese caro. But the direct/indirect distinction is useful everywhere, because the two families produce genuinely different shapes.
What a direct reply does
When O plays directly beside X — say at h9 — O's mark blocks one of X's four directions immediately: the column through h8 now has an O mark right next to it on one side. O's mark shares X's column; the row and both diagonals through h8 remain entirely open for X.
The typical consequences:
- X tends to develop sideways and diagonally, away from the blocked column.
- O's mark sits on the same line as X's mark, so the two players' shapes start tangled along that column.
- Games often become sharp and tactical quickly, because both players' marks interfere with each other at close range.
What an indirect reply does
When O plays diagonally — say at i9 — O's mark sits on one of X's diagonals. X's row and column remain completely open, and the other diagonal too.
The typical consequences:
- X can build rows and columns freely, which are the directions beginners see most easily.
- O's mark is slightly less "in the way", but it occupies a diagonal that X would otherwise use.
- The early game is often a little calmer, with both sides building shape before the first threats appear.
Which is better for O?
Neither is objectively better for casual play; both are perfectly sound. What matters is that O understands what the reply does:
- A direct reply fights X's shape at close range along one line. Choose it if you like tactical, tangled games.
- An indirect reply takes a diagonal and leaves X more room along rows and columns. Choose it if you prefer to build your own shape a little before the fighting begins.
Many beginners find the indirect reply easier because it leaves the easy-to-see directions (rows and columns) open for both players, while the diagonal O occupies is precisely the direction beginners tend to miss.
X's third move
Whatever O chooses, X's third move follows the principles from gomoku opening principles:
- stay close to both marks,
- add to two potential lines at once,
- avoid growing into O's mark.
Against a direct reply at h9, natural third moves include g8, i8, g7 and i7 — points that build a row or diagonal with h8 while keeping away from O's column. Against an indirect reply at i9, natural moves include h9, g8, i8 and h7 — points that build X's open row or column while crowding O's diagonal mark.
You will see strong players choose all sorts of third moves. What they share is that each move does more than one job.
Under blocked ends
Under Vietnamese caro rules, a direct reply has a small extra effect: O's mark sits right at one end of any future X line along that column through h8. That line is already half blocked, so O needs only one more mark at the other end later to kill it permanently. This makes direct replies slightly more attractive in blocked-ends play.
A short direct opening, move by move
To make the difference concrete, here is a plausible short direct opening described in words.
- X plays h8.
- O plays h9, directly above.
- X plays i7, diagonally below-right of h8. It builds X's anti-diagonal (h8–i7) and stays away from O's column.
- O plays g9, the other end of that anti-diagonal (g9–h8–i7), which also makes a row two with O's own h9.
- X plays i8, beside h8. Now X has a row two (h8–i8) and a column two (i7–i8), both heading into open space on the right.
After five moves the shapes are already tangled: O's two marks sit on two of X's lines, and X is steering its development toward the side of the board O has not touched.
A short indirect opening
- X plays h8.
- O plays i9, diagonally above-right.
- X plays h9, next to O's mark and above its own. X now has a column two and crowds O's diagonal.
- O plays h10, blocking X's column from above while making a two with i9 on a diagonal.
- X plays g8, building a row two (g8–h8) and a diagonal two (g8–h9).
Here the opening developed more calmly: each player built pairs of twos, and the first real threats are still a few moves away. In both examples, notice how every X move after the first adds to two lines — the principle that matters far more than any named sequence.
Practise the difference
Play a set of games as O against the computer on the home board: five where you always answer the centre directly, five where you always answer diagonally. Notice which feels more comfortable and in which set the computer's attacks develop faster. If you sign in to your account, you can replay all ten openings side by side afterwards.
Frequently asked questions
What is a direct opening in gomoku?
An opening where the second mark is placed directly beside the first — on the same row or column.
What is an indirect opening?
An opening where the second mark is placed diagonally next to the first.
How many renju openings are there?
Renju uses 26 standard openings: 13 direct and 13 indirect, defined by the position of the third stone.
Do I need to learn renju openings to play caro?
No. For freestyle gomoku and Vietnamese caro, understanding the two families is enough.
