Ultimate Tic Tac Toe — free online against the computer

Nine small boards arranged in a big three-by-three. Win a small board and you claim that square of the big one; win three big squares in a row and you win the game. The twist that makes it a real game: the cell you play in decides which small board your opponent has to play in next.

Play in the top-right cell of any board and they must answer in the top-right board. If that board is already finished, they can play anywhere. Your score is wins in a row, and the computer searches one step deeper every time you beat it. Free, no download, no sign-up.

How to play

• The board you must play in is outlined in yellow and everything else is dimmed. That is the only thing you need to read.
• Win a small board — three in a row inside it — to stamp it as yours.
• Three stamped boards in a line wins the game.
• If you are sent to a finished board, you may play anywhere. That is the free choice, and giving one away is the most common mistake.
• If nobody has a line when the boards run out, whoever won more small boards takes it; a genuine tie ends the run, the same as a loss.
• Your score is consecutive wins, and your top 5 is kept on this device.

Every move is two moves, and the second one is the one that loses games

Ordinary noughts and crosses is solved: two people who know what they are doing draw every time, which is why the version of it on this site had to be built as a streak against a computer that deliberately errs. Ultimate Tic Tac Toe is not solved, and the reason is the send rule. A position is not just nine boards; it is nine boards plus the answer to "where am I allowed to play?", and that answer is set by your opponent's last move.

So every move you make is really two decisions. The first is the obvious one: is this a good square on this board? The second is the one beginners never see: where does playing here send them? A move that completes a line for you but sends your opponent into the board where they are about to complete two is a losing move that feels like a winning one.

Three habits follow, and they will win you games immediately.

Do not hand out free choices. When you play into a board that is already decided, your opponent gets to play anywhere on the grid. That is the single most valuable thing in the game and you should almost never give it away deliberately. If you are forced to, pick the moment.

The centre board is worth more than it looks, for the same reason the centre square is in ordinary noughts and crosses: it sits on four of the eight winning lines, while a corner sits on three and an edge on two. That weighting is exactly what the computer here uses to judge a position, and it is why it fights so hard for the middle.

Watch for the board that sends to itself. Playing in the centre cell of the centre board sends your opponent to the centre board. Playing in the top-left cell of the top-left board sends them to the top-left board. Those self-referential moves keep the fight in one place, which is useful when you are winning there and dangerous when you are not.

More games

More from ♟️ Board games vs computer:

• Chinese Checkers — Ten pegs each on the full star. Build a ladder of pegs and hop the whole board in one move.
• Nine Men's Morris — Place nine, form a mill, take one of theirs. Down to three pieces and you can fly.
• Four in a Row — Beat the computer and it thinks one move deeper next game. How long can the streak last?
• Reversi — Flip your opponent's discs to your colour. Take the corners — and beware the squares beside them.
• Checkers — Captures are compulsory — which is exactly how you set traps. Beat it and it thinks deeper next game.

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