Tic-Tac-Toe strategy

Perfect play never loses. Learn which squares matter, the right reply to every opening and the forks that beat players who slip.

Understanding the game

Tic-Tac-Toe is a solved game: there is a known strategy that guarantees at least a draw for both players, and with perfect play from both sides every game ends in a draw. Most people don’t play perfectly, though, and that is where the wins come from.

Which squares matter

A square is worth roughly as much as the number of winning lines that pass through it.

The center: 4 lines
More than any other square. It controls the board, limits your opponent’s options and is the classic first move.
Corners: 3 lines each
Strong in attack and defense, and two opposite corners work especially well together. The other good opening, and the right reply when the center is taken.
Edges: 2 lines each
The weakest squares. Take one when you need it to block or to win, and avoid it as an opening.

Going first (X)

The center
The classic opening. Your opponent has to answer with a corner; an edge loses.
A corner
Just as safe and harder to defend: the only reply that doesn’t lose is the center.
An edge
The weakest opening. It still draws with good play, but it sets the fewest traps.

If you start in the center

They take a corner
Take the opposite corner. They must answer with another corner; if they take an edge, you can make a fork.
They take an edge
Take a corner. From here every corner wins: you force a block, then make a fork.

If you start in a corner

They take the center
Take the opposite corner. Now they must play an edge; if they take a corner, you can make a fork.
They take another corner
Take one of the two corners left. They have to block, and your next corner makes a fork.
They take an edge
Take the center, or a corner that makes two in a row. Either way you force a block and then fork.

On this site

X always moves first, and in a rematch the other player starts, so you practice both sides. Against the computer on Unbeatable you will never win, but you can check that your defense holds.

Going second (O)

Your priorities, in order

  1. 1
    Win if you can: always take a winning move.
  2. 2
    Block their two in a row.
  3. 3
    Make a fork of your own if one is available.
  4. 4
    Block their fork before they can make it.
  5. 5
    Take the center if it’s free and nothing above applies.
  6. 6
    Take a corner rather than an edge.

If they start in the center

Take a corner
The only reply that keeps the draw.
Never take an edge
It is a weak defensive square, and it loses to a fork.
Make them respond
When you get the chance, make threats of your own so they have to block.

If they start in a corner

Take the center
The strongest defensive square, and the only reply that keeps the draw.
Then watch the far corner
If they take the opposite corner next, answer with an edge, not a corner. A corner lets them fork.
Keep your options open
Holding the center stops them controlling the board and leaves you the most choices.

Advanced concepts

Creating forks

A fork is two ways to win on your next turn. Your opponent can block only one of them.

  • Opposite corners give you several fork chances.
  • Three corners make two lines along the sides of the board.
  • The center and two corners combine a diagonal with a row or column.

Blocking forks

  • Make your own threat so they have to block it, as long as their block doesn’t give them a fork.
  • Block early. Take the square they need before the fork exists.
  • Defend with two in a row. Choose a threat that leaves them no fork in reply.

Forced moves

Two in a row forces your opponent to block. Chain forced moves together to steer the game where you want it, and look two or three moves ahead to see whether the chain ends in a fork.

Common winning patterns

Corner opening

  1. 1
    X takes the top-left corner.
  2. 2
    O takes the top edge next to it. This is the mistake.
  3. 3
    X takes the center, threatening the diagonal.
  4. 4
    O must block in the bottom-right corner.
  5. 5
    X takes the bottom-left corner, threatening both the left column and the other diagonal. O can block only one, and X wins.

Center opening

  1. 1
    X takes the center.
  2. 2
    O takes the top edge. This is the mistake.
  3. 3
    X takes the top-left corner, next to O’s edge, threatening the diagonal.
  4. 4
    O must block in the bottom-right corner.
  5. 5
    X takes the bottom-left corner, threatening the left column and the other diagonal. That is a fork, and X wins.

Common mistakes

Taking edges early
Edges are weak. Put the center and the corners first.
Missing an obvious block
Every turn, check whether your opponent can win next move.
Missing your own win
Check whether you can win right now before anything else.
Ignoring fork threats
Notice when your opponent is setting one up.
Playing too defensively
When you have a winning move, take it.
Not thinking ahead
Consider the position your move leaves behind.

Ready to play?

Practice the traps against the computer on Easy, test your defense on Unbeatable, or invite a friend.

Play Tic-Tac-Toe