About Tic-Tac-Toe
Tic-Tac-Toe (Noughts and Crosses) is a two-player classic on a 3×3 grid. Take turns marking squares; the first to line up three of their marks wins. Our "Unbeatable" computer uses the minimax algorithm — the best you can do against it is a draw.
How to play well
Tic-Tac-Toe is small enough to be solved completely, which is exactly what makes it interesting to practise: there is a correct move in every position, and the game is really about spotting the threat you cannot see yet.
- Take the centre if it is free. It sits on four of the eight winning lines — more than any other square.
- Then take corners, not edges. A corner sits on three winning lines; an edge sits on only two.
- Look for forks. A fork is a move that creates two threats at once, so your opponent can only block one. Against the Easy computer this is how almost every win happens.
- Block before you build. If your opponent has two in a line, block it — a win you were one move away from is worth nothing if they get there first.
Against the Unbeatable computer none of this wins, because perfect play by both sides always ends in a draw. Holding it to a draw every time is the real test.
Frequently asked questions
Can I beat the unbeatable computer?
No — it plays perfectly. With best play, Tic-Tac-Toe always ends in a draw, so aim for a draw against Unbeatable, or switch to Easy mode for a winnable game.
Is the running score saved?
Yes. The X / O / draw tally is saved locally in your browser until you tap "Reset score". Nothing is uploaded.
What is the minimax algorithm?
It is a method for playing a solved game perfectly. The computer looks at every possible continuation to the end of the game, assumes you will always play your best reply, and picks the move with the best guaranteed outcome. On a 3x3 board this is quick enough to do on every turn.
Who has the advantage, X or O?
X moves first and so has more chances to create a fork, which makes X easier to play. Neither side can force a win against perfect defence, but a mistake by O is punished more often than a mistake by X.
Can I play against another person?
Yes. Switch the mode to "2 players" and both X and O are played by hand on the same device, with the computer taking no part.