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Renju Forbidden Moves: 3-3, 4-4, Overlines and False Forbidden Points

Renju exists because plain gomoku favors the first player too much. To balance it, Black, who moves first, is barred from three kinds of moves, while White plays freely. The rules below follow the Renju International Federation (RIF) definitions as we implemented them in Hanpan, and every ✕ and ○ in the pictures is confirmed by the game's forbidden-move code.

The short version

A Black move that makes exactly five wins even if it also creates a double three or double four. Five comes first.

Definitions that matter

• Four: one more stone turns the line into five. A four blocked on one end is still a four.
• Open four: an unbroken four that can become five at either end.
• Three: one more stone turns the line into an open four, and that stone must neither make five nor be a forbidden point itself.
• Double three / double four: one stone creates two or more threes (or fours) at once.

A double four on one line

Two fours do not need two lines. If one line has two different points that each complete five, it counts as two fours. This is the forbidden move new renju players miss most often.

False forbidden points

A three must be able to become an open four. If the only point that would make that open four is itself forbidden for Black, the line cannot really grow, so it is not a three. A move that looks like a double three may then have only one real three, and it is legal. Deciding whether the extension point is forbidden can require checking its own threes in turn, so the test is recursive. Hanpan repeats it up to six levels deep and has test positions for two-level cases.

What happens on a forbidden move

In official renju, Black loses immediately by playing a forbidden point, and White may deliberately steer Black into a spot where the only defense is forbidden. Hanpan marks forbidden points with a red ✕ and blocks them, so you cannot lose by a slip; but if the point you must block is marked ✕, White has the win.

Openings

Tournament renju adds an opening procedure in which the first stones follow set patterns and players get a chance to swap colors. Hanpan leaves that procedure out: Black's first stone goes on the center (H8) and play is free after that. The game labels this rule "Renju (no opening rules)".

New to the game? Start with Gomoku rules. Korean: 렌주룰 금수.

More rules guides

한국어 안내: 장기 두는 법 · 장기 상차림 · 오목 33 금지 규칙 · 렌주룰 금수

Written and drawn by the Js at JWorld. Rule details vary between clubs and apps; this guide follows the rules used in Hanpan. Boards are drawn in code, with no generative-AI images.