Forbidden moves exist to blunt Black's first-move advantage. Once you know which rule sets apply them, it becomes clear why the same move loses on the spot in one game and is the strongest move available in another.
Black moves first on the 15×15 board, and that single tempo matters more than it looks. In 1993 L. Victor Allis proved that freestyle gomoku is a first-player win — with best play on both sides, Black wins.
Renju (the RIF rules) closes that gap by restricting Black alone. White plays under no restrictions and wins with five or more in a row. A forbidden move is less a list of fouls than a tax on moving first.
In each diagram the outlined stone is the move just played. Under Renju, Black loses on the spot for playing it; under freestyle all three are ordinary moves.
One move that creates two open threes at once. The opponent can only block one of them, so an open four is guaranteed next move.
Under Renju, Black loses on the spot for playing it. Under freestyle it is not a foul at all — it is the first winning technique most players learn.
One move that creates two fours at once. The blocking points split in two, and stopping either one lets the other reach five.
Like the double-three, Renju forbids it to Black only; in freestyle it is a legitimate way to finish.
Six or more stones in an unbroken line.
In Renju an overline by Black is a loss, not a win. Freestyle counts five or more as a win, so an overline wins there too, while under exact five that line alone does not win.
The rule sets Gomoku Mate offers, side by side. Check the winning condition of the rules you picked before starting a game. The tournament rule ‘Gomoku · Swap2’ is scored exactly like Exact five: no forbidden moves, and an overline is not a win for either color. It balances the game through the opening instead, by letting the other player choose a color after the first three stones.
| Rules compared | Freestyle | Exact five | Renju (RIF) |
|---|---|---|---|
| Five in a rowExactly five stones of the same color in an unbroken horizontal, vertical or diagonal line. | Win | Win | Win for both |
| Six or more (overline)A line carried past five in the same direction. | Win | Not a win on that line alone | Loss for Black, win for White |
| Double three (3·3)One move that creates two open threes. | Allowed | Allowed | Forbidden to Black only |
| Double four (4·4)One move that creates two fours. | Allowed | Allowed | Forbidden to Black only |
| Who is restrictedWhich side the forbidden moves apply to. | Neither | Neither | Black |
Freestyle and exact five treat neither a double-three, a double-four nor an overline as a foul. Black and White play under the same conditions, and the only difference between those two is whether six or more counts as a win. Ending a game with "that move was illegal" is a poor way to learn, and the double-three is the first winning shape most players pick up.
Pick Renju and Black is bound by the double-three, double-four and overline rules. On Black's turn the board marks the points Black may not play with ✕ and prevents those moves; the marks can be turned off in the settings. With them off, a forbidden move loses the game on the spot for Black. The forbidden-point rules use the same definition as the AI engine, so the AI's moves and the marks never disagree.
Renju comes in two forms. “Renju” applies the forbidden rules only, and every stone may go anywhere. “Renju · official opening” adds the RIF tournament regulation: the first stone is played on the center point, the second stays inside the 3 × 3 square around it, the third inside the 5 × 5 square, and after the third stone White chooses once whether to take Black instead. For the fifth move Black offers two squares and White picks one. In an AI game the AI decides for itself while it holds White; in an online room White gets the buttons. Two players at one screen simply swap seats.
Turn on hints and the recommended move is drawn out step by step, showing which attack it leads to. AI practice is available under every rule set.
Read the rules and tactics guideIt depends on the rules. Freestyle and exact five allow double-threes and double-fours; Renju forbids them for Black alone, and even there White plays freely.
Under freestyle it does. Under exact five that line alone does not win, so when five is available, avoid running past it to six.
Because Black moves first. Freestyle gomoku is a proven first-player win, so Renju forbids Black the double-three, double-four and overline to restore the balance.