How to Never Lose at Tic Tac Toe

You cannot force a win against a careful opponent. You can force a draw. 'Never lose' means: follow a short policy so every line that would beat you is blocked in time.

If you go first (X)

Start in a corner or the center. Then, for every later move, run this scan: win, block, stop their fork, make your fork, take center if free, take a corner, take a side. Do not get clever and skip the scan because a corner 'looks nicer.'

If you go second (O)

If X took the center, take a corner. If X took a corner, take the center. If X took a side, take the center. After that, the same scan as X: win, block, fork, center, corner, side.

The trap people miss

X starts in a corner. O takes a side cell instead of the center. X can now force a fork. That is the most common 'I thought I was fine' loss. Taking the center as O against a corner opening is the single highest-value habit in the game.

How to train it

Play Tic Tac Toe against Hard AI. You will not win. You should draw, repeatedly. If you lose, rewind the last three moves: you skipped a block or you allowed a fork. The minimax explainer shows why the computer never skips those.