Gomoku, known in Korea as Omok, looks simple, but sites differ in which moves they forbid. This post explains the standard rules most common in Korean online Omok. Gomoku on Gamengager follows these rules.
The basics
- Play on a 15×15 board. Black moves first, then players alternate.
- The first player to line up exactly five stones horizontally, vertically or diagonally wins.
Three key points
1. Double-three is forbidden for both players
You may not play a move that creates two open threes at once. An open three is three stones with open ends that become an unstoppable open four with one more move.
Under the Korean standard rules this restriction applies to both Black and White. That is the biggest difference from Renju, which restricts only Black.
2. Double-four is allowed
A move that creates two fours (four stones that make five with one more move) at the same time is legal.
3. Six or more does not win
An overline of six or more stones does not count as a win. You need exactly five.
Compared with Renju
| Rule | Korean standard | Renju |
|---|---|---|
| Double-three | Forbidden for both | Forbidden for Black only |
| Double-four | Allowed | Forbidden for Black only |
| Overline | Does not win | Forbidden for Black, wins for White |
Things to remember in play
- A move that completes five is always allowed, even if it also makes a double-three.
- White cannot play double-threes either, so knowing your opponent’s forbidden points helps you defend.
- A four-three (a four plus an open three in one move) is legal and is the most reliable way to win.