Стратегия игры в крестики-нолики

To win tic-tac-toe, go first and start in a corner, then try to create a fork: a move that makes two lines of two at once, so your opponent can block only one. To never lose, learn the right reply to each opening: answer a corner with the centre, the centre with a corner, and always block a fork before it happens. With perfect play from both sides the game is always a draw. Test yourself against the unbeatable computer in the free Tic-Tac-Toe game.

We checked every line below by computer, searching all 255,168 possible games.

The three kinds of square

The board has nine squares, and they're not equal:

• Centre: on four lines (a row, a column and both diagonals).
• Corners: on three lines each.
• Edges (the middle of each side): on only two lines each.

More lines means more chances to make threats, which is why the centre and corners are stronger than edges.

Rule 1: Win if you can, block if you must

Every turn, check in this order:

1. Can you complete a line? Do it.
2. Can your opponent complete a line next turn? Block it.
3. Can you make a fork? Do it.
4. Can your opponent make a fork next turn? Stop it, ideally by making a two-in-a-row that forces them to block you instead.

Most casual games are lost at step 2: someone misses a block. Most "good player" games are decided at steps 3 and 4.

Как это сделать win tic-tac-toe with a fork

Here's a real example. You're X and start in the top-left corner. O takes the centre. You take the bottom-right corner. O now makes a mistake and takes the top-right corner, threatening the diagonal from top-right to bottom-left.

You must block in the bottom-left corner, but look what that block does: you now threaten the left-hand column and the bottom row at the same time. O can stop only one, and you complete the other. That double threat is a fork, and it's the only way to beat a player who never misses a simple block.

Going first: the corner opening

Opening in a corner is the most testing start. Of the eight replies, only the centre avoids a loss for O. If your opponent plays anything else, there's a forced win:

• O takes the opposite corner: take one of the two remaining corners. You threaten a line and will set up a fork.
• O takes an edge or an adjacent corner: you can also force a win, usually by taking another corner that creates a threat and then a fork.

If O correctly takes the centre, the game should be a draw, but there's still a trap. Take the opposite corner. Now O must reply on an edge; if O takes a corner instead, you can fork and win.

Going first: the centre opening

Starting in the centre is solid. Here O must reply in a corner: any edge reply loses. After centre, then a corner from O, try the corner opposite O's. Now O has to take another corner; an edge loses.

Edge openings are the weakest start for X, though still not a losing one.

Going second: how to never lose

You'll often move second. In our game, X and O take turns starting each new game, so against the computer you play second every other game. The safe replies:

Opponent opens	Your safe reply	Replies that lose
Corner	The centre	Any other square
Centre	Any corner	Any edge
Edge	The centre, either corner next to it, or the opposite edge	The other four squares

Then keep applying Rule 1. Two further traps to remember when playing second:

• You have the centre and X has two opposite corners: play an edge, not a corner.
• X has the centre and the corner opposite yours: take another corner, not an edge.

Playing the computer

Choose Against the computer and a level:

Level	How it plays	Can you win?
Easy	Often places marks at random	Yes, often. Practise setting up forks.
Medium	Usually plays the best move, sometimes slips	Yes, when it slips. Punish mistakes.
Unbeatable	Always plays a perfect move	No. A draw is the best result.

On Unbeatable, your goal is never to lose. If you can draw ten games in a row, including the ones where the computer moves first, you've learned the game. The score for each side and the draws are kept in your browser; Reset score clears them.

Choose Two players to play a friend on the same device, which is great for teaching children the fork idea.

Why perfect tic-tac-toe is a draw

Because the board is so small, every position can be worked out completely. When both sides follow the rules above, no one ever gets a fork that can't be stopped, so the game always fills up with no line. That's why tic-tac-toe is a good first strategy game: you can master it in an afternoon.

For a bigger challenge built on the same "make two threats at once" idea, try Four in a Row. Our guide on how to win Connect 4 shows how forks work on a bigger board.

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Pick Unbeatable and see if you can hold it to a draw from both sides. The free Tic-Tac-Toe game runs in your browser with no download or sign-up.