How to Never Lose at Tic Tac Toe (and When You Can Win)

Tic tac toe (noughts and crosses) is usually the first strategy game anyone learns, and it is small enough to be completely solved: with perfect play, every game is a draw. That does not make it pointless. Knowing the right moves means you will never lose, and you will win every time your opponent slips. Here is the complete method.

The rule that decides every move

On every turn, run through this checklist and play the first item that applies:

1. Win: if you have two in a line with the third square empty, take it.
2. Block: if your opponent has two in a line with the third square empty, take it.
3. Fork: make a move that creates two lines of two at once. Your opponent can only block one.
4. Block a fork: if your opponent could make a fork next turn, stop it, ideally by making a two-in-a-line of your own that forces them to block.
5. Centre: take the centre if it is free.
6. Opposite corner: if your opponent holds a corner, take the opposite one.
7. Corner: take any free corner.
8. Edge: take an edge square.

Following this order perfectly means you never lose. Most beginner losses come from skipping step 2 or step 4.

Playing as X (first)

Open in a corner

A corner is the strongest practical opening. The only safe reply for O is the centre. Any other reply lets X force a win:

• If O takes an edge, X can usually set up a fork within two moves.
• If O takes the opposite corner or an adjacent corner, X takes another corner and threatens two lines.

Or open in the centre

The centre is part of four lines (both diagonals, the middle row and the middle column), so it is also a fine opening. O’s best reply is a corner; an edge reply gives X good fork chances.

The classic corner trap

X plays a corner. If O replies on an edge next to it, X takes the centre, threatening the diagonal. O must block, and X then takes a corner that creates two threats at once. O cannot stop both.

Playing as O (second)

As O, your goal is a draw unless X makes a mistake.

X opens in…	Your best reply	Why
A corner	The centre	Every other reply loses to good play
The centre	A corner	An edge reply gives X easy forks
An edge	The centre (or a corner next to the edge, or the opposite edge)	The centre is simplest and safe

The opposite-corners trap

A common position: X has two opposite corners and O holds the centre. Here O must play an edge, not a corner. Taking a corner lets X fork using the two remaining corners. Playing an edge forces X to block, and the game heads to a draw.

Why forks are everything

Since a single threat can always be blocked, the only way to win against a careful player is to create two threats in one move. Corners are valuable precisely because each one sits on three lines (a row, a column and a diagonal), which gives the most fork chances. Edges sit on only two lines, which is why they are the weakest squares.

Quick reference

Situation	Move
You have two in a line	Complete it
They have two in a line	Block it
You can make two threats at once	Do it (fork)
They could fork next turn	Force them to block a threat of yours
Centre is free	Take it
They hold a corner	Take the opposite corner
Nothing else	Corner, then edge

Teaching it to children

Tic tac toe is a great first lesson in thinking ahead. Ask two questions before every move: “Can I win?” and “Can they win next turn?” Once those become habits, introduce forks, and let them try the corner trap against you. A child who can see a fork coming has learned the same skill that wins at Four in a Row, checkers and chess.

Practise against the computer

The tic tac toe game on this site has three levels:

• Easy always takes a win but plays a random move most of the time: practise setting forks and the corner trap.
• Medium plays perfectly most of the time but slips now and then, so you must spot the one chance it gives you.
• Unbeatable searches every possible game with a full minimax search, so it never loses. Drawing against it consistently proves your defence is perfect.

When 3×3 feels solved, try Five in a Row on the 15×15 board, where you need five marks in a line. The same ideas apply on a bigger scale: block early, build threats in two directions, and look for a move that creates two open lines at once.