Tic-Tac-Toe

Tic-Tac-Toe is the game most of us learned on a scrap of paper. Here it comes in three board sizes, so it stays interesting after the first few games: the small board is a quick warm-up, and the bigger boards need real planning.

How to play

You play the orange crosses. The computer plays the blue rings. Tap an empty square, or click it with the mouse, to place your mark. The computer answers at once.

The first player to line up the required number of marks wins. The line can run across, up and down, or on a slant. If the board fills up and nobody has a line, the game is a draw.

Who starts changes from game to game. When the computer starts, it makes its mark before you do anything.

The levels

The level sets the size of the board, the length of line you need, and how well the computer plays.

• Easy: a 3 by 3 board, three in a row. The computer slips a lot and often forgets to block you. Undo is on.
• Medium: a 3 by 3 board, three in a row. The computer plays well, but it still slips now and then. Undo is on.
• Hard: a 4 by 4 board where you need four in a row. The computer searches deeply and is hard to beat. There is no undo.
• Expert: a 5 by 5 board, again with four in a row to win. The computer searches as deep as its time allows. There is no undo.

On the bigger boards a line of four is not the full width, so there are many more ways to build one, and more ways to be surprised.

Today's game

There is a Medium game each day, on the 3 by 3 board. Everyone gets the same game, including who makes the first mark. Start it with the "Today's game" button on the new game card.

Tips

1. On the 3 by 3 board, take the center if you can. If the computer has already taken it, a corner is the next best square.
2. Always check whether the computer is one mark short of a line. Block it unless you can win on the spot.
3. The way to beat a careful player on the small board is a fork: a move that makes two lines at once. The computer can only block one.
4. When you play second on the 3 by 3 board, answer a corner start with the center. Answering with an edge square tends to lose.
5. On the 4 by 4 and 5 by 5 boards, watch for three in a row with an empty square at each end. That is as good as a win, because you cannot block both ends.
6. Bigger boards are about space. Play where your marks can grow in more than one direction, and do not push into a corner where lines are short.
7. Perfect play from both sides on the small board always ends in a draw. If you manage a draw against the computer on Medium, you played well.

A bit of history

A similar three-in-a-row game was played in ancient Rome, so this is one of the oldest games on the site.

Questions

Why does the board change with the level? The small board is the classic. The bigger ones give people who have outgrown it something harder.

How long a line do I need on the big boards? Four in a row, on both the 4 by 4 and the 5 by 5 board. Only the small board needs three.

Can the game end in a draw? Yes, on every level.

Who plays first? It alternates, so each of you gets turns at both.