KarHow to play Reversi
Reversi begins with four discs at the centre of an 8×8 board. Place a disc to enclose an unbroken opposing line between two of your own, then flip that line. The aim is to own the most discs when neither player can move.
Start a game
- Black starts from the standard four-disc opening.
- Choose a highlighted legal square.
- Enclose at least one opposing disc along a row, column or diagonal.
- Every enclosed line flips to your colour.
- When neither side has a legal move, compare disc counts.
Legal moves and flips
A move must enclose at least one uninterrupted line of opposing discs, with your newly placed disc at one end and an existing disc of your colour at the other. All lines enclosed by that move flip.
Placing a disc that captures nothing is not legal. You cannot move an existing disc to another square; every normal turn adds a new disc to an empty square.
Passing, winning and the clock
If you have no legal move, your turn is passed and your opponent plays again. One player passing does not end the game. It ends when neither player can move; the larger disc count wins, with equal counts producing a draw.
You have 40 seconds per move. If time expires, the game chooses a random legal move. A considered move is safer than leaving a corner decision to the timer.
Example: the opening
At the standard start, Black has four legal moves. Each encloses one White disc. After the first move, Black has four discs and White has one. Those four openings are symmetric; the later choices create the meaningful differences.
A large early disc count does not establish a winning position. Ask how many legal moves the opponent will have after your move and whether one of them gives away a corner.
Mobility, corners and difficulty
Corners cannot be flipped once secured. Squares beside an empty corner can be dangerous because they may let the opponent take it. Stable edges and limited opposing mobility are often more important than flipping the largest possible number immediately.
Easy bots choose random legal moves. Medium values corners, avoids dangerous corner neighbours and considers mobility. Hard also examines the opponent’s best reply. Improve by comparing available moves for both players, not just today’s score.
Strategy and useful habits
- Protect access to corners.
- Count the opponent’s options after a move.
- Avoid grabbing many discs merely to lead early.
- Treat a forced pass as an opportunity to improve position.
Common mistakes
- Trying to place a disc without flipping anything.
- Assuming one pass ends the game.
- Giving away a corner for a temporary disc advantage.
- Waiting until the clock makes a random move.
Questions and answers
Who starts?
Black always starts from the standard centre arrangement.
What if I cannot move?
Your turn passes. The game ends only when neither player has a legal move.
How is a draw decided?
If both players have the same number of discs at the end, the result is a draw.