Omok Guide

Why a One-Minute Rule Turns Everyone Serious

Omok takes about a minute to learn. Get five of your stones in a row (horizontal, vertical, or diagonal) before your opponent does, and you win. Sit two people down at a board, though, and the mood turns serious fast. Every stone you place immediately becomes a potential threat, so there's really no such thing as a "throwaway move." Omokboard itself started as a way to play Omok with a friend. The other games came later.

Omokboard's Omok uses free-style rules. There are no forbidden moves like Renju's 3-3 or 4-4 bans, so both sides can play however they like.

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Objective & Basic Rules

• The goal is simple: be the first to place five stones in an unbroken row, horizontally, vertically, or diagonally.
• Black moves first, then players alternate. Black has a slight edge, so if White lets up on defense early, the game can slip away fast.
• Stones never move or get captured once placed. A line of six or more still counts as a win as long as it contains five in a row.
• Each move has a 30-second limit. If you run out the clock, the turn simply passes to your opponent.

The Five Threat Levels: Learn This Order and You're Halfway There

Every bit of reading in Omok comes down to judging one thing: what threat level is this shape right now?

• Open two: two in a row with both ends open. Not a threat yet, but the seed of an attack.
• Open three: three in a row, both ends open. Leave it alone and it grows into an open four next move.
• Open four: four in a row with both ends open. Block one end and the other still completes five, so the game is essentially over.
• Closed four: four in a row open on only one end. You can still block it, but miss that one spot and you lose immediately.
• Double threat (four-three, double-three): one move that creates a four and a three, or two open threes, at once. Your opponent can only block one, making this the single strongest winning shape in Omok.

Opening: Why Everyone Crowds the Center

A stone in the center can extend in four directions: horizontal, vertical, and two diagonals. A stone in the corner has far fewer directions to work with, so no matter how well you connect it, it struggles to build real threats. That's why the first few moves almost always cluster near the center: claim a spot that can grow in every direction before chasing anything flashy.

Midgame: Hunt for Where Two Directions Cross

This is where skill gaps actually show. Just extending one line is easy to stop, because your opponent only has to block one end. The real strength move is stacking stones at an intersection where two different directions (say, a row and a diagonal) both pass through, quietly setting up a spot where one more move creates two threats at the same time. Once you reach that point, whatever your opponent blocks, they still lose.

Defense: Block in the Wrong Order and One Move Ends It

• Priority one: always block a four immediately. Open or closed, one late move and it's over.
• Priority two: stop an open three before it grows into an open four. The most dangerous moment is thinking "it's only three stones" and letting it sit.
• When you have several options to block, pick the one that also builds your own attack. That way you get defense and offense in a single move.

Watch for the Trap: When a "Weak" Move Isn't Weak

Strong players rarely open with an obvious threat. They often play something that looks harmless on purpose, baiting you into an automatic block. That very block is what completes a double threat somewhere else on the board. Before you block anything, take one extra beat to ask: does blocking here make some other spot even more dangerous?

How Omokboard's AI Plays

Knowing how each difficulty level thinks makes the AI a much better practice partner.

• Easy looks only one move ahead. It scores every spot for its own attack and for blocking yours, then picks at random from the top five. That's why it sometimes leaves an obvious three alone, and now and then even misses your four.
• Normal reads two moves ahead: its move and your reply. It always takes a winning spot and always blocks a five you could finish next move, but it can't see a double threat you're preparing further out.
• Hard reads four moves ahead. As it searches deeper, it keeps only the 12 most promising spots at each step, so it builds double threats on its own and cuts off the ones you're setting up.

One odd detail: the Hard AI moves the fastest. The pause before each AI move is a delay added on purpose (1.2 seconds on Easy, 0.5 on Normal, 0.1 on Hard), so the easier the AI, the more it looks like it's thinking.

Even the Person Who Built It Loses to the Four-Three

I've played a lot of Omok since I was a kid, at school and at home, and against Omokboard's Hard AI I still win only about half the time. When I lose, it's almost always the same way: the AI plays a four-three (one move that makes a four and an open three at once), and I only notice once it can no longer be stopped.

A four-three gives itself away a few moves early. Look for an empty point where your opponent's closed three and open two, running in different directions, would meet. That point is the next target. One stone there turns the closed three into a four and the open two into an open three. A closed three rarely feels urgent, so it's easy to leave alone, but the "four" in a four-three usually grows out of exactly that neglected three. When nothing urgent is happening, start by scanning for empty points where two of your opponent's lines cross.

Training by Skill Level

Just starting out? Play the Easy AI and focus purely on recognizing the five threat levels by sight. Winning matters less right now than being able to tell an open three from a closed one at a glance.

Getting comfortable with the rules? Move to Normal AI and build the habit of checking both "my threats" and "their threats" every single move. Missing an opponent's four while chasing your own attack is the most common mistake at this stage.

Can you already build a double threat? Move to Hard AI and train your defense. The Hard AI creates double threats on its own, so simply holding your ground against it will sharpen your play fast.

Curious why free-style rules became standard, and why Renju exists at all? Read the history and origins of Omok.

FAQ

• Does Black always win? Black has a slight first-move advantage, so White needs to defend carefully from the very start.
• Does six in a row count? Yes. Omokboard's free-style rules count any line containing five or more.
• Isn't 3-3 illegal? It's forbidden under tournament Renju rules, but Omokboard uses forbidden-move-free style, so anyone can play it.
• What's the fastest way to improve? Memorize the five threat levels, and always deal with your opponent's biggest threat first, every move.
• How many moves ahead should I think? At first, checking just one move ahead (can my opponent win right now?) is enough. Once that's comfortable, practice looking two moves out to see whether your next move sets up a double threat.