Tic-Tac-Toe

What is Tic-Tac-Toe?

Tic-Tac-Toe on Rocket Games is the paper-and-pencil classic, drawn by hand on your screen: every X and O is sketched stroke by stroke and the winning line is scored right through the row. Play the computer at three levels, from Easy, which leaves openings, to Impossible, which plays perfectly and can never be beaten, or hand the phone to a friend and play two players on one device.

When three in a row gets too easy, switch to Ultimate Tic-Tac-Toe: nine small boards inside one big one, where the square you choose decides which board your opponent must play next. It turns a solved children's game into a real strategy game. Both modes keep a scoreboard, let you undo a move or ask for a hint, can be played entirely from the keyboard, and save your game so you can come back to it later.

How to play Tic-Tac-Toe

1. Choose Classic 3×3 or Ultimate at the top, then pick your opponent: the computer at Easy, Medium or Impossible, or 2 players on one device.
2. Choose who goes first: you, the computer, or alternate each game. Against the computer you play X.
3. Tap a square to place your mark. Players take turns; the first to get three in a row, across, down or diagonally, wins. A full board with no line is a draw.
4. In Ultimate, the square you play sends your opponent to the matching small board: the glowing board is where the next move must go. If that board is already won or full, any open board is allowed.
5. Win a small board with three in a row inside it; win the game with three small boards in a row. Use Undo to take back a move, Hint for a suggestion and New game to start over.

Tic-Tac-Toe tips and strategy

• In classic tic-tac-toe, start in a corner. It gives the other player the most ways to go wrong; the only safe reply is the centre.
• If your opponent takes a corner first, take the centre. Any other reply loses against best play.
• Look for forks: a move that makes two lines of two at once. The other player can only block one of them.
• In Ultimate, think about where you are sending your opponent before you think about the square itself. A great square that sends them to a board they can win is a bad move.
• In Ultimate, the centre board and the centre square of each board are worth the most, because they sit on the most lines.
• Sending your opponent to a board that is already won or full gives them a free choice of board. Avoid it unless every alternative is worse.

How to win (or never lose) at tic-tac-toe

Tic-tac-toe is a solved game: if both players make no mistakes, every game ends in a draw. That is why the Impossible level can't be beaten. It searches every possible continuation before each move, so the best you can do is draw. To stay safe yourself, follow three rules in order on each turn: complete your own line if you can, block your opponent's line if they threaten one, and otherwise make a move that creates two threats at once or stops your opponent from doing so.

Wins come from forks. As X, taking a corner first and then the opposite corner sets up forks against an opponent who replies on an edge. As O, answer a corner with the centre, and answer a centre opening with a corner. Easy and Medium make the kind of mistakes people make, so they are good for practising these patterns.

Ultimate Tic-Tac-Toe rules in detail

The big board is a 3×3 grid of small tic-tac-toe boards. The first move can go anywhere. After that, the position of the square you play inside its small board names the small board your opponent must play in next: play the bottom-left square and they must reply somewhere in the bottom-left board. Getting three in a row inside a small board wins it, and the whole board is marked with your symbol. Once a small board is won or completely full, nobody can play in it again, and a player sent there may choose any open board instead.

The game is won by taking three small boards in a row, across, down or diagonally. If every small board is decided and neither player has a line of three boards, the game is a draw. Ultimate is far too large to solve by brute force, so the computer uses Monte Carlo tree search, playing out thousands of random games in a background thread to judge each move. Easy thinks for a fraction of a second and sometimes plays at random, Medium thinks for under a second, and Expert takes about two seconds a move.

A short history of noughts and crosses

Three-in-a-row games are thousands of years old, and the paper version was being played in England as noughts and crosses by the nineteenth century. The name tic-tac-toe became the usual one in the United States in the twentieth century. It was also one of the first games ever played by a computer: OXO, written in 1952 for the EDSAC computer at Cambridge, played noughts and crosses against a human. Ultimate Tic-Tac-Toe is much newer, a puzzle-hunt and classroom favourite that spread widely online in the 2010s.

Tic-Tac-Toe FAQ