How to play Tic-tac-toe
You play crosses against the computer's rings. Take turns placing one mark on an empty square. The first to get a full line of their own marks, across, down or corner to corner, wins. If the board fills with no line, it is a draw.
The boards
- 3 × 3: three in a row wins.
- 4 × 4: four in a row wins, so every line is a whole row, column or diagonal.
- 5 × 5: four in a row wins, and a line can start anywhere it fits.
Every one of these boards ends in a draw if both sides play perfectly. Who moves first swaps from one game to the next.
The computer
- Easy takes a win most of the time but often forgets to block, so it leaves lines open for you.
- Medium always takes a win and always blocks, and sets up two ways to win about half the time it can.
- Hard plays the best move every time. On 3 × 3 and 4 × 4 it never loses; a draw is the best result against it.
The owl
On each of your turns the owl names the best square and why: a win that is open, a line of the computer's that must be blocked, a trap to avoid. Tap No hints to play without it. Undo takes back your last move, and Restart begins the board again.
How to win
- Open in the centre on 3 × 3 and 5 × 5. The centre sits on more lines than any other square.
- Block a line the moment the computer is one mark away from a full line. Nothing else matters until that square is covered.
- Make two ways to win at once. A move that opens two lines, each one mark from complete, wins: the computer can block only one. This is called a fork.
- Stop two ways to win. If the computer can make a fork with its next move, take that square first, or make a line of your own that forces it to answer you instead.
- One short of a line forces a block. While the computer is busy blocking, it cannot build its own lines.
On the 3 × 3 board, the corners are the next-best squares after the centre: each sits on three lines, and an edge square sits on only two.