How to Win Tic Tac Toe: Openings, Forks and Blocks
Updated
You cannot beat a tic tac toe player who makes no mistakes: if both sides play perfectly, the game always ends in a draw. What you can do is never lose, and win whenever your opponent makes a mistake that allows it. To do both, check a short list before every move: win, block, fork, block their fork, center, opposite corner, corner, side.
The rules in 30 seconds
- Two players take turns marking a 3×3 grid, one with X and one with O.
- X usually goes first, although there is no fixed rule about it.
- Three of your marks in a row, a column or a diagonal wins.
- If all nine squares fill up with no line of three, the game is a draw, often called a cat's game.
To talk about moves, number the squares like a phone keypad. Squares 1, 3, 7 and 9 are the corners, 5 is the center, and 2, 4, 6 and 8 are the sides.
| Left | Middle | Right |
|---|---|---|
| 1 | 2 | 3 |
| 4 | 5 | 6 |
| 7 | 8 | 9 |
Why perfect play is always a draw
There are only three really different first moves: a corner, a side or the center. Turn the board and every corner looks like every other corner, and every side like every other side.
Whichever of the three X picks, O has at least one reply that holds the draw. After that, careful play from both sides fills the board without a line of three. The game is small enough for a computer to check every possible game, and a 1952 tic tac toe program called OXO was one of the first known video games.
The move order that never loses
Before each move, go down this list and make the first move that applies. This order comes from a tic tac toe program written by Allen Newell and Herbert Simon in 1972.
- Win: if you have two in a line and the third square is empty, take it.
- Block: if your opponent has two in a line, take the third square yourself.
- Fork: make a move that creates two lines of two at once. Your opponent can block only one of them.
- Block their fork: if your opponent could make a fork next turn, take that square. If they have two possible forks, make two in a row instead, so they must answer you, and check that their forced answer does not give them a fork.
- Center: take square 5.
- Opposite corner: if your opponent holds a corner, take the one across from it.
- Empty corner: take any free corner.
- Empty side: take any free side square.
Steps 1 and 2 keep you from losing in the short term. Against anyone who always blocks, step 3 is the only way to win: a fork makes two threats, and a player can stop only one.
Going first: how X wins
Against a perfect O you will draw, so choose the opening that gives O the most ways to go wrong. After a corner opening, O has only one safe reply: the center. If O takes a side or another corner, you can force a win.
Here is how it works when O answers with a corner. You play 1 and O plays 3. You play 7, which threatens 1-4-7, so O must take 4. Now you play 9: you threaten 7-8-9 and 1-5-9 at once, and O can block only one.
If O answers your corner with a side, take the center. You play 1, O plays 2, and you play 5, so O must block at 9. Then you play 7 and threaten 1-4-7 and 3-5-7 together.
After a center opening, O must answer with a corner. If O takes a side instead, say 2, you play 1, O must block at 9, and your move to 7 makes the same fork as above.
Between perfect players the first move makes no difference. A corner gives O the fewest safe replies, while one study found the center works better against players who make mistakes.
Going second: how O never loses
- Answer a corner with the center. If X then takes the opposite corner, play a side square, not a corner.
- Answer the center with a corner.
- Answer a side with the center, a corner next to X's mark, or the side opposite it.
- After the opening, follow the move order above, and watch for forks above all.
As O you win only when X makes a mistake that allows it. When that happens, the same list finds the win for you.
Common mistakes
- Answering a corner opening with anything but the center.
- As O, taking a corner on your second move after X has taken the corner opposite their first one. X blocks with a move that also makes a fork.
- Making two in a row in a way that lets your opponent block and create a fork with the same move.
- Chasing your own line and forgetting to block.
Practice against the computer
Tic Tac Toe Pro has an AI with different skill settings, so you can test the move order against its stronger levels. Cat Tic Tac Toe lets you play another person or the AI, with an optional undo button. XO With Buddy is the plain game: line up three of your symbols to win.
Tic Tac Toe Glow also has a 5×5 grid where you need four in a row. Forks and blocks still decide that game, but the opening advice above is for the 3×3 board.
When the 3×3 grid stops surprising you, try 4 in a row - Board game for 2 players, where you connect four tokens of one color. More quick duels are in the 2-player category and the brain collection, and forced moves matter even more in how to play checkers.
Common questions about tic tac toe
Is tic tac toe always a draw?
With perfect play from both sides, yes. Between people it can go either way, because one wrong reply in the opening can lose by force.
How do you win tic tac toe going second?
Only when X makes a mistake that allows it. Answer the opening correctly, follow the move order, and take the win as soon as X leaves one.
Can you beat the computer at tic tac toe?
Only if it makes a mistake. A program that plays perfectly can always force at least a draw, so look for wins on the easier settings.
Learn the eight-step move order once, and as long as you follow it, you will not lose a game of tic tac toe.
