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Connect Four

Drop counters down a seven-column grid and line up four, against a computer at three strengths or a second player.

You

0

Computer

0

Draws

0

Your turn.

You are Red

Tap a column to drop a counter. Four in a row wins — across, down or diagonally.

Plays entirely in your browser · no sign-up, no download

Connect Four — Where the Board Is Big Enough to Matter

Connect four looks like tic tac toe with more squares. It is a much deeper game, and the reason is gravity: you do not choose a square, you choose a column, and your counter lands on top of whatever is already in it. Every move you make builds the platform your opponent plays from.

That single rule produces the game's whole character. A threat you cannot complete yet still has to be respected, because the square below it may get filled at any moment. Playing under an opponent's winning square hands it to them. And two threats stacked in the same column can only be answered once. Where tic tac toe has 255,168 possible games and is completely solved in the head, connect four has over four trillion positions — it has been solved by computer, but not by anyone sitting at a table.

The computer opponent searches ahead: two moves on easy, four on medium, seven on hard. Between those depths it judges a position by how many lines of four are still open to each side, weighted so three-with-a-gap counts for far more than three scattered pieces. At seven plies hard sees a double threat being set up before it exists, which is the point at which most people stop winning by accident and start having to plan. Easy is beatable on purpose: it sometimes plays a random column instead of its best one, and while it always takes a win in front of it, it will not always block yours.

Two players on one device is the other mode, and the columns are tappable anywhere down their height — you do not have to aim at the one live cell, which matters on a phone. The score above the board tracks both sides plus draws, and whoever starts alternates between games, since the first move is worth something here too. In fact connect four is a first-player win with perfect play from both sides, which is exactly why a fair run of games has to swap it.

The winning four is highlighted when a game ends, including the diagonals, which are the ones that catch people out.

How to play Connect Four

  1. Choose Easy, Medium or Hard, or "Two players" for someone on the same device.
  2. Tap anywhere in a column to drop your counter — it lands on the lowest free row.
  3. Line up four in any direction: across, down, or either diagonal.
  4. Watch what your move leaves above it. Filling a square under your opponent’s winning row hands them the game.
  5. The winning four is highlighted, and the score above the board keeps a running total.

Questions

How strong is the computer?

It looks two moves ahead on easy, four on medium and seven on hard. Hard will see and stop a double threat while you are still setting it up; easy sometimes plays at random and does not always block.

Can two people play on one device?

Yes — tap "Two players". You take turns dropping counters on the same board, with the score kept for both sides.

Who has the advantage, red or yellow?

Whoever moves first. With perfect play from both sides connect four is a win for the first player, which is why the starting side alternates between games here.

Do I have to tap the exact square?

No. Tapping anywhere in a column drops a counter into it, the way the physical game works — which is much easier on a phone than aiming at one cell.

Is it free, and does it need an app?

Free, with no account and no download. It is a few kilobytes of JavaScript running on your own device, and it keeps working if the connection drops.