Tic Tac Toe

How to play

Take turns claiming squares on the three by three grid. First to line up three of their mark in a row, column or diagonal wins, and a full grid with no line is a draw. Play a friend on the same device, or take on the computer at three strengths. On Perfect the computer searches the whole game tree, so it never loses. The best you can force against it is a draw, which is exactly what makes it worth trying.

Tips

• Open in a corner against a human. It sets more traps than the centre and most people answer it wrong.
• If you move second and they took the centre, take a corner. Taking an edge loses against decent play.
• Against the centre opening, the only safe replies are corners. Edges hand over a fork.
• Look for forks, where one move creates two lines at once. Your opponent can only block one of them.
• Perfect play by both sides is always a draw, so on Perfect a draw is a win.

A game that is always a draw

Tic tac toe has been fully analysed for as long as people have played it: with correct play from both sides it always ends in a draw. There are only 255,168 possible games, small enough that a computer can examine every one, which is what the Perfect opponent here does. It searches the entire game tree from the current position, so it never loses. The best you can force against it is a draw, and forcing that draw consistently is a real skill.

Easy and Hard are the same search with a chance of playing a random move instead, so they can be beaten. The win streak is tracked per difficulty, since a streak against Easy and a streak against Perfect are not the same achievement.

Playing it correctly

• First move: corner or centre. An edge opening is the only one that lets a good opponent take the initiative.
• If your opponent opens in the centre, take a corner. An edge reply loses by force.
• Look for forks: a move that creates two lines at once. Only one can be blocked.
• Block a fork before it exists. If your opponent has two open lines that share an empty square, take that square.
• A draw against Perfect is a win in every sense that matters. It cannot lose, so holding it to a draw is the ceiling.

Common questions

Can the Perfect computer be beaten?

No. It searches every possible continuation from the current board and never plays a losing move. A draw is the best possible result against it.

How many possible games are there?

255,168 when every distinct sequence of moves is counted, which is why the whole game can be searched instantly.

Why does my win streak reset when I change difficulty?

Streaks are tracked per opponent strength, so an Easy streak cannot inflate a Perfect record.