Connect Four

About Connect Four Online

Connect Four was invented in 1974 by Howard Wexler and Ned Strongin and first published by Milton Bradley. It is often described as a vertical version of Tic Tac Toe, but the gravity mechanic makes it far deeper strategically. Because pieces drop to the lowest empty slot in each column, you must plan your moves in layers — what looks like a harmless column could be setting up a diagonal win three turns later. The game was mathematically solved in 1988 by Victor Allis, who proved that the first player can always win with perfect play.

The center column is the most important position on the board. From the center, your pieces can build chains both left and right, while edge columns limit you to building in one direction. A common winning strategy is building two separate three-in-a-row chains at once — your opponent can block only one. Good players also think about the order in which columns fill. Dropping into a column that already has three pieces is useless because there is no room to complete four. The game becomes an exercise in managing column height as much as pattern recognition.

Connect Four has a fascinating legacy in artificial intelligence research. Victor Allis's 1988 proof that the first player can force a win was a significant milestone in combinatorial game theory. His solution showed that by playing the center column on the first move and responding correctly to every counter, the first player can always connect four before the opponent. This makes Connect Four a "first-player win" game with perfect play — unlike Tic Tac Toe which is a draw. The game was later completely solved by the University of Alberta in 1995, which published the complete solution tree for every possible board position.

Our AI adapts to your skill with three difficulty levels. Easy mode makes predictable moves and rarely builds advanced threats — perfect for learning the basics and practicing column management. Medium mode provides a balanced challenge for casual to intermediate players, blocking immediate threats while building its own attacks. Impossible mode is extremely demanding — it uses deep minimax search with alpha-beta pruning to evaluate every reasonable move multiple turns ahead. The game also includes an optional 2-minute timer for players who want to test their decision-making under pressure.

Play against the AI or challenge a friend locally on the same device. No login required — games are free to play, and ads may appear around the page, not during a move. Just fast, responsive Connect Four in your browser. For the dedicated vs-AI landing with Easy to Impossible tactics, try Connect Four vs AI. For more alignment-based strategy, try Gomoku (Five in a Row) on a 15x15 board.