Play Connect Four Online for Free
Connect Four is the disc-dropping duel where every move is a small act of gravity. Played on a standing 7-column, 6-row grid, you and your opponent take turns sliding colored discs into open columns, each one tumbling to the lowest empty slot. Red always drops first, and the race is on to line up four of your own discs in a row — across, up, or on either diagonal — before your opponent does the same. The catch is that you never choose the exact square, only the column, so every threat is shaped by the stack beneath it.
How to Play Connect Four
Connect Four is a two-player game on a vertical grid that is 7 columns wide and 6 rows tall. One side plays red discs, the other plays yellow, and red always takes the first turn. On your turn you pick any column that is not already full; your disc drops straight down and settles on the lowest empty slot in that column. You can never place a disc in mid-air or choose its exact height — gravity decides the row for you.
You win the instant you connect four of your own discs in an unbroken line. That line can run horizontally along a row, vertically up a single column, or diagonally in either direction. The engine checks all four orientations after every drop, so a sneaky diagonal counts exactly the same as an obvious horizontal four. There is no limit on how many discs each player has — you keep dropping until someone connects four or the board runs out.
If all 42 slots fill up and neither player has made four in a row, the game is a draw. There are no captures, no removing discs once they land, and no passing — every turn you must drop somewhere. You can play against the computer at three difficulty levels or share one device with a friend in local two-player mode, and an undo button lets you take back your last move while you are learning.
Playing Against the Computer
All three levels use the same search and evaluation. Easy looks up to two moves ahead and picks at random among its four best moves, Medium looks up to four moves ahead and picks between its two best, and Hard searches as deep as 1.5 seconds allows and always plays the best move it finds. Every level takes a win it can see and avoids a loss it can see when it has another move. Its evaluation rewards lines of four holding two or three of its discs and no opposing disc, counts your open lines against it, and adds a bonus for each of its discs in the center column.
That evaluation ignores which row a threat sits on, so an odd/even threat that only pays off beyond its search depth is your best weapon; against Hard, expect to need forcing sequences rather than a simple oversight.
Frequently Asked Questions
Do diagonal lines of four really count as a win here?
Yes. The engine checks horizontal, vertical, and both diagonal directions after every disc lands, so four in a row on either diagonal wins exactly like a horizontal or vertical line. Diagonal threats are the ones players miss most often, both when attacking and when defending.
Who goes first, and does that decide the game?
Red always drops first. Connect Four is mathematically solved — with flawless play the first player can force a win by opening in the center column. In practice, perfect play is extremely hard, so going first is an edge rather than a guarantee, especially against the medium and hard AI.
Can I take a disc back or remove one from the board?
Discs are permanent once they land — there are no captures and no removing pieces mid-game. However, the undo button takes back your most recent move, together with the computer's reply when you play against it, which is handy for studying lines or recovering from an obvious slip.
What happens if the whole board fills with no four in a row?
It is a draw. The board has 42 slots, and if every column fills without either color connecting four, neither player wins. There is no passing and no tiebreaker — a full board with no line is simply a tie.
How do the three AI difficulty levels actually differ?
All three use the same search and evaluation, which favors the center, but think for different lengths of time and choose differently. Easy thinks briefly and picks at random among its four best moves, Medium thinks longer and picks between its two best, and Hard thinks longest and always plays the best move it finds — so it punishes loose threats hard. Every level takes a win it can see and avoids a loss it can see when it has another move.