Alignment · rules · components · playable model

Tic-Tac-Toe

A compact perfect-information game for examining alignment, blocking, forks, forced replies, symmetry, and solved play.

Model focus

Small state spaces make it possible to see how one move can create several future threats at once.

placementalignmentperfect informationforced replies
Players2
Time1–5 min
Weightintroductory
Rules

How does this ruleset work?

Be the first player to place three of your marks in one horizontal, vertical, or diagonal line.

This page models the common three-by-three ruleset with X moving first.

01

Set up

  1. 1Place an empty three-by-three grid between the two players.
  2. 2Choose one player to use X and the other to use O. X moves first in this model.
02

Take a turn

  1. 1Place one mark in any empty space.
  2. 2Marks never move or leave the board after placement.
  3. 3Players alternate turns unless the game has already ended.
03

End the game

  1. 1A player wins immediately when three of their marks share a row, column, or diagonal.
  2. 2If all nine spaces fill without a winning line, the game is a draw.
Component inventory

What is in the box?

Component packaging varies by edition and manufacturer. This inventory lists the functional pieces required by the modeled ruleset.

× 1
Three-by-three board

Defines the nine legal spaces and eight possible winning lines.

× 5
X markers

One player's pieces; five are enough to fill every X turn in a full game.

× 4–5
O markers

The other player's pieces; physical sets often include a spare.

Playable rules model

Simulate the game locally.

This is a same-device two-player model. It enforces legal placement, captures, turn changes, win conditions, and other rules described above.

table state

X to place a mark.

The simulator stops as soon as a winning line appears.