How to play Tic-Tac-Toe

Tic-Tac-Toe — also known as Noughts and Crosses — is the little pencil-and-paper game everyone learns as a child. Here you play it against a computer opponent, with no download and no sign-up. The board is a simple 3×3 grid of nine squares. You and the bot take turns claiming squares, one with X and one with O, and the first to line up three of their own marks wins the game.

The goal

Get three of your marks in a straight line — across a row, down a column, or along either diagonal. If all nine squares fill up and nobody has a line, the game is a draw. X always moves first.

How to play

• Tap or click any empty square to place your mark there.
• The bot replies straight away with its own move.
• The winning line is highlighted the moment someone completes three in a row.
• Your running tally of wins, losses, and draws is kept on this device.

Choose your side and difficulty

You can play as X to take the first move and press the attack, or as O to defend against the bot's opening. When you start a new game you can also pick a difficulty. On Easy the bot mostly plays at random and will happily let you win. On Medium it always takes a winning move and always blocks yours, but does not look further ahead. On Hard it runs a complete minimax search of every possible continuation, so it never makes a mistake.

Strategy and the perfect-play secret

Played perfectly by both sides, Tic-Tac-Toe is always a draw — so against the Hard bot, a draw is a genuine victory. The strongest opening square is the centre; corners are the next best, and edges are weakest. Watch for "forks", where a single move creates two winning threats at once that your opponent cannot both block. The Hard bot will set up forks against you and shut down yours, so the only way through is flawless defence. If you ever see it win, it caught a slip — the Easy and Medium bots leave far more room to outplay them.