How to play
Two players take turns placing their mark, X or O, in an empty square. On the classic 3×3 board the first player to get three marks in a row across, down or diagonally wins. If all nine squares fill up with no line, the game is a draw.
Choose Computer to play against the machine or 2 players to share one screen with a friend. The score boxes above the board keep a running tally of wins and draws, and the highlighted box shows whose turn it is. When a game ends, tap anywhere on the board to start the next one. On a keyboard, move between squares with the arrow keys and press Enter to play.
The three computer levels
- Easy picks squares at random. Good for young kids learning the game.
- Medium takes a win when it sees one and usually blocks yours, but otherwise makes mistakes about half the time.
- Unbeatable searches every possible game from the current position. It never loses on 3×3.
The 5×5 board
The bigger board changes the goal: you need four in a row to win. There are 28 possible winning lines instead of 8, games last longer, and draws are less common. Blocking one threat is not enough if your opponent can build two at once.
Strategy tips
Opening
On 3×3, the center square is part of four winning lines, each corner is part of three, and each edge square only two. That is why the best first moves are the center or a corner. If your opponent opens in a corner, take the center; any other reply can lose by force.
Make a fork
A fork is a move that creates two threats at once. Your opponent can block only one, so you win on the next turn. A classic example: X takes the top-left corner and O answers on the top edge next to it. X takes the center, threatening the diagonal, so O must block the bottom-right corner. X then takes the bottom-left corner and threatens both the left column and the other diagonal. Against perfect defense no fork is possible, which is why the game always ends in a draw between two careful players.
Defend in the right order
Every turn, ask three questions in this order. Can I win right now? Can my opponent win on the next move, and can I block it? Can I create a fork, or stop one?
Tips for 5×5
Stay near the middle. A mark in the center row or column fits into far more four-in-a-row lines than one on the edge. Watch for open threes: three in a row with both ends empty means your opponent has two ways to finish it.
Variants and fun facts
There are 255,168 different ways a game of 3×3 tic tac toe can be played out to the end, counting every order of moves. Gomoku is the big-board relative, played on a large grid where five in a row wins. In misère tic tac toe the player who makes three in a row loses. Ultimate tic tac toe nests nine small boards inside one large board, and where you play on a small board decides which board your opponent must play next.
For a step up in depth, try Four in a Row, where gravity decides where your disc lands, or Dots and Boxes.
Questions
Can you beat the Unbeatable level?
No. On the 3×3 board it checks every possible continuation, so the best you can get is a draw. A draw against it means you played perfectly too.
How do you win on the 5×5 board?
You need four of your marks in a row, across, down or diagonally. Five in a row also counts, since it contains four. The computer on Hard looks a few moves ahead on this board but it can be beaten.
Who goes first?
Use the First move buttons. In computer mode you are always X; choose You, Computer, or Take turns to alternate who opens each game.
Is the score saved?
Yes, the tally for each board and mode is kept in your browser on this device. Press Reset score to clear it.