How to play Tic Tac Toe: rules and strategy

Everyone knows how to play tic tac toe, but few people know how to never lose. This guide covers the rules, then the four ideas that decide every game: corners, the centre, forks and blocking forks.

The rules

Tic tac toe, also called noughts and crosses or Xs and Os, is played on a grid of three by three squares. One player is X and the other is O.

1. X goes first. Players take turns placing their mark in any empty square.
2. Three in a row wins: across, down or along either diagonal.
3. A full grid with no line of three is a draw, often called a cat’s game.

On BoardGameSite players take turns being X from one game to the next, so you get the first move every other game. Tap a square to play, or press 1 to 9 on a keyboard, counting from the top left.

The three kinds of square

Not all squares are equal. The centre is part of four lines (one row, one column and both diagonals). Each of the four corners is part of three lines. Each of the four edges (the middle square of each side) is part of only two. The more lines a square belongs to, the more ways it can help you win and the more of your opponent’s lines it can block.

Strategy: playing first (X)

Start in a corner. The centre is a fine first move too, but a corner gives your opponent more ways to go wrong. If O answers anywhere except the centre, X can force a win.

Then take the opposite corner. If O played an edge or a corner, a second corner usually sets up a fork on your third move.

Start in the centre for a safe game. From the centre X can’t lose, and if O answers on an edge rather than a corner, X can force a win.

Strategy: playing second (O)

Answer a corner with the centre. If X starts in a corner, the centre is the only reply that doesn’t lose against perfect play.

Answer the centre with a corner. If X starts in the centre, take a corner. An edge reply lets X build a fork.

Answer an edge with the centre. An edge opening is X’s weakest start. The centre, either corner next to X’s edge, or the opposite edge are all safe replies.

Forks: how games are won

A fork is a move that makes two lines of two at once, each with its third square empty. Your opponent can only block one of them, so you complete the other next turn. Almost every game of tic tac toe that isn’t a draw is won with a fork.

The classic fork for X: corner, then the opposite corner, then a third corner. With X in three corners, two lines are threatened at once.

Blocking forks

When you can’t win, look at where your opponent could fork next turn and stop it. There are two ways:

• Play on the fork square yourself. If there is only one square where they could fork, take it.
• Force them to block you. Make a line of two so they must answer it, choosing a line whose empty square isn’t one of their fork squares. This is the key defence when X holds two opposite corners and you hold the centre: play an edge, not a corner, so X has to block on the other side.

The order of priorities

Perfect play follows a simple checklist, top to bottom:

1. If you can make three in a row, do it.
2. If your opponent can make three in a row next turn, block it.
3. If you can make a fork, do it.
4. If your opponent can fork next turn, block the fork.
5. Otherwise take the centre, then a corner (ideally opposite your opponent’s), then an edge.

The Hard computer follows rules like these, which is why it never loses.

Common beginner mistakes

• Answering a corner opening with anything other than the centre.
• Blocking one line of two without noticing the fork your opponent is building.
• Answering X’s two opposite corners with another corner instead of an edge.
• Rushing to make a line of two when it forces your opponent onto the very square they wanted.

Tic Tac Toe FAQ