Gomoku

Black plays first. Stones go on the intersections rather than in the squares, and once placed they never move and are never captured. The first player to line up five of their own stones in a row — horizontally, vertically or diagonally — wins.

That is the whole game, and it is why the interesting part is what happens before the five. Four in a row with both ends open cannot be blocked: whichever end your opponent takes, you play the other. So most of Gomoku is about making two threats at once, and about spotting when your opponent is one move from doing the same.

Show threats marks every point where the other side would complete a line on their next move. It is off by default on purpose — it does a real part of the thinking for you.

Two rule sets, and they are never mixed. Freestyle is the version almost everyone means by Gomoku: five in a row wins, and so does six or more. Exactly five wins on five and not on six — an overline is not a win, and play carries on. The difference only ever shows up when a stone fills a gap to make six without ever having made five, and when it does it decides the game.

There are no forbidden moves. Tournament Gomoku, or Renju, restricts black — no double-three, no double-four, no overline — to offset the advantage of moving first. Zerdly does not implement those, so black keeps that advantage and nothing on this board is illegal except playing on an occupied point.

The 15 × 15 board is the standard one. 19 × 19 is the same rules with far more room, which makes it slower and much harder to corner somebody on. Changing either the board or the rules starts a new game, and each combination keeps its own record.

Undo takes back your last stone — against the computer it also takes back the reply. Show coordinates labels the files and ranks; both assist settings are remembered between visits. Sound can be turned off at any time; nothing in the game is conveyed by sound alone. A game in progress is saved as you play and is waiting when you come back.

Versus the computer gives you six strengths. The weaker ones do not merely look less far ahead — they sometimes choose a move they can see is not the best, which is what makes them feel like an opponent rather than a machine with poor eyesight. The strongest never does.

Two players, one device takes the computer out of it entirely. These games are counted but not scored: both players are here, so there is nobody for Zerdly to call the winner.

Daily puzzle is one position a day, the same for everyone on the same UTC date. Exactly one move forces a win, and that is proved before the puzzle is offered: every move on the board is played out against every possible reply. A wrong guess costs nothing and is not held against you.

An open three is the move that wins games. Three in a row with both ends free becomes an open four next turn, and an open four cannot be stopped — so your opponent has to answer a three immediately, which means you get to choose where the game happens.

Count your opponent’s threats before your own. Almost every lost game of Gomoku is one where somebody built a beautiful attack one move too slowly. If they have a four, you have exactly one legal reply, and it does not matter what you were planning.

Play towards the middle early. A stone near the edge sits on fewer lines than one in the centre, and lines are the only currency in this game.

The whole game runs in your browser. The opponent thinks on your own device and the daily puzzle is generated and proved there too, both in background threads so the page stays responsive while they work. No account is needed and nothing about your game is uploaded.

Your record, your saved game, your daily results and your sound, motion and assist settings are stored in this browser only. Nothing here asks for a name or an email, and the button on this page removes all of it — and only this game’s share of it.

Is it really free, and do I need an account?

Yes, and no. There is no sign-up, no trial and nothing to buy. The game runs in your browser and never sends your moves anywhere.

Does six in a row win?

It depends which rules you chose, and that is the whole difference between them. Under Freestyle, five or more wins — six is a win. Under Exactly five, an overline is not a win at all and the game simply carries on. The rule set is shown next to the board and is saved with your game.

Are there any forbidden moves for black?

No. Tournament Gomoku — Renju — forbids black from making a double-three, a double-four or an overline, to offset the advantage of moving first. Zerdly does not implement those restrictions, so nothing here is forbidden and black keeps that advantage.

What is the daily puzzle?

One position a day, the same for everyone, generated from the UTC date rather than downloaded. Before it is offered, every move on the board is checked against every possible reply, so exactly one move is a forced win. A wrong guess costs nothing.

Can I play against another person online?

No. Two-player here means two people at the same device, taking turns. There is no matchmaking and no online play, and nothing on this page pretends otherwise.

How strong is the computer?

The weakest level looks one move ahead and often plays something it can see is not best. The strongest looks eight moves ahead over the twelve most promising points. It never considers a point far from every stone, which is what makes a board of 225 intersections searchable at all.

Where is my progress kept?

In this browser, and nowhere else. Each board size and rule set keeps its own record, because they are not the same game. Clearing your browser data, or using the button on this page, removes all of it permanently.

• Four in a RowSix opponents, a daily position and tactical puzzles.
• ReversiSix opponents, an analysis board and solved endgame puzzles.
• Nine Men's MorrisLine up three and take a piece. Six opponents and proved puzzles.