About Ultimate Tic Tac Toe

Learn more about the game on Wikipedia.

How to Play

Objective: Win three small boards in a row (horizontally, vertically, or diagonally) on the large 3x3 meta-board.

Setup: The game is played on a 3x3 grid of smaller 3x3 Tic Tac Toe boards, creating 81 total cells.

Gameplay:

• The first player can place their mark (X) in any cell on any of the nine small boards.
• After the first move, each player's move determines which small board the opponent must play in next.
• The position of your mark within a small board corresponds to which small board your opponent must play in. For example, if you play in the top-right cell of any small board, your opponent must play somewhere in the top-right small board.
• If a player is sent to a small board that is already won or full (tied), she may play in any open cell on any available board.
• To win a small board, get three of your marks in a row within that board (just like regular Tic Tac Toe).
• Once a small board is won, it counts as that player's mark on the meta-board. The cells in a won board can no longer be played in.
• The game ends when a player wins three small boards in a row on the meta-board, or when all small boards are decided (resulting in a tie if neither player has three in a row).

The AI

It works like DeepMind's AlphaZero. A neural network learned the game by playing itself, with no human games or tips. On its turn, a tree search uses the network to size up moves and plays the best one it found.

It all runs in your browser. Expert thinks for 2 seconds a move, so it's a bit stronger on a faster device, and Very strong looks a few moves ahead. Both first check for a win within their next two turns, so they never miss one. The other levels don't look ahead at all. Strong plays whatever looks best right now, and each level below it picks more at random, down to Random, which plays any legal move. The Analysis page shows what it makes of any position.

Its estimate of who's winning counts draws too: between good players, about half the games are drawn.