Renju Rules Explained: Forbidden Moves and Tournament Play
If you’ve played enough Gomoku, you’ve probably noticed something: black wins a lot. Like, a lot a lot.
This isn’t a skill issue. It’s a mathematical reality. At competitive levels, the first-move advantage in unrestricted Gomoku is substantial. Black wins roughly 60–70% of games between strong players.
I first ran into this while testing the AI on this site. Black against Medium? Comfortable win. Switch to white against the exact same opponent — suddenly every game is a desperate scramble. That asymmetry bugged me enough to dig into how competitive players deal with it. The answer is Renju.
Renju was created to solve this.
What Is Renju?
Renju (連珠, “connected pearls”) is the competitive version of Gomoku. It was formalized in Japan in 1899 by the Nihon Renju Sha (日本連珠社), the first organized Renju association, to address the imbalance in standard play.
The core innovation: forbidden moves for black.
Every rule of standard Gomoku still applies. The same board. The same basic win condition: five in a row. But Renju adds specific moves that black is not allowed to make. If black makes a forbidden move, black loses immediately.
(White plays under standard rules — no restrictions.)
The Forbidden Moves
There are three categories of forbidden moves for black in Renju:
1. Double Three (3-3)
Black cannot place a stone that simultaneously creates two or more open threes.
An open three is three stones in a row with empty spaces on both ends. Creating two of them at once is devastating in standard Gomoku — and illegal in Renju.
2. Double Four (4-4)
Black cannot create two or more open fours in a single move.
3. Overline (6+ in a Row)
Black cannot win with a line of six or more stones. In standard Gomoku, overlines are simply ignored. In Renju, creating an overline as black is a loss.
Important: What Black CAN Do
Black can create:
- A single open three (3)
- A single open four (4)
- A three-and-four combination (3-4) — this is the primary way black wins in Renju
- A straight five to win
The restrictions are specifically on multiples of the same threat type. Notice the difference between the forbidden 3-3 above and the legal 3-4 below — in 3-4, the threats are different types, so it’s allowed.
Opening Rules
To further balance the game, Renju tournaments typically use an opening protocol that goes beyond simple “black goes first.” The most common is the Swap Opening:
- The first player places three stones — two black and one white — anywhere on the board.
- The second player then chooses which color to play. If they think black’s position is too strong, they take black. If they think white has compensation, they take white.
This clever system forces the first player to create a position that’s roughly balanced — because if they give black too much of an advantage, their opponent will simply take black.
Some tournaments use more complex protocols (Swap2, Soosyrv-8), but the principle is always the same: let the players balance the opening themselves.
Why Play Renju?
Renju is to Gomoku what tournament Chess is to casual Chess: a formalized, balanced version that rewards deep study and precise play.
If you find standard Gomoku starting to feel lopsided — especially when you or your opponent always plays black first — Renju offers a fairer, more competitive experience.
Is Renju on This Site?
Our current game engine uses standard Gomoku rules (no forbidden moves), which is the right place for beginners to start. If there’s enough interest from the community, adding Renju mode with swap openings is high on our development list.
Back to the basics? Read How to Play Gomoku.