Reversi
Play Reversi on an 8 × 8 board against three CPU levels or a friend on the same device. Practise corners and mobility with legal-move hints and a match recap.
Reversi
Play Reversi on an 8 × 8 board against three CPU levels or a friend on the same device. Practise corners and mobility with legal-move hints and a match recap.
About Reversi
Flipping stones on an 8 by 8 board
The game starts with the standard four center stones on an 8 by 8 board. A legal move must trap one or more opponent stones in a straight line across any of the eight directions, then those trapped stones flip to your color.
Reading the legal moves
The four center stones start interlocked, which always gives Black exactly four legal moves. A legal move is not any empty square: the stone you place must trap opponent stones in some direction, with one of your own stones closing that line. The board highlights every playable square by default, and the setting can be switched off once you no longer need it.
The few principles that decide the game
A stone in a corner can never be flipped, because a corner has no far side in any direction and nothing can trap it. That also makes the squares next to a corner risky, since they tend to hand the corner over. Holding fewer stones in the midgame is often an advantage: fewer stones means fewer legal moves for your opponent, who is then forced into the squares you want. The Normal computer here scores positions purely by stone count, so taking the most stones every turn is exactly how it plays, and exactly what mobility beats; the Strong computer values corners, edges and mobility instead.
Local CPU mode and game end
When a player has no legal move, the turn passes automatically; the game ends when neither side can move, and the side with more stones wins. The computer has three levels: Easy plays a random legal move, Normal runs a shallow minimax on stone count, and Strong searches a few moves ahead with corner, edge and mobility weights and plays the last few moves out exactly. All of it runs locally in the browser, intended for casual play rather than official Othello rating or online match history.
FAQ
Common questions and answers about this topic.
How do you play Reversi on this board?
Place a stone on an empty square where it traps at least one opposing stone in a straight line horizontally, vertically or diagonally. Every trapped stone flips to your color. The game starts with the standard four stones in the center.
Can I play Reversi against the computer?
Yes. Pick Easy, Normal or Strong in the lobby and choose whether you play Black (moving first) or White. Easy plays random legal moves, Normal takes the most stones every turn, and Strong fights for corners and mobility and plays the endgame out exactly. Everything runs in your browser, so it is a casual opponent rather than a rated engine.
Can two people play Reversi on the same device?
Yes. Choose Two players in the lobby and take turns placing Black and White stones on the same board; Black always moves first. Both stone counts, the corners each side holds and whose turn it is stay visible, and the result card offers a rematch when the board is full.
What happens when a player has no legal move?
The turn passes automatically if the other player still has a legal move. You do not need to press a pass button. If neither player can move, the game ends and the final stone counts decide the winner.
How is the winner decided in Reversi?
The game ends when neither Black nor White has a legal move. The player with more stones on the board wins; equal counts produce a draw. The live score above the board shows both counts throughout the game.
Does taking more stones mean you are winning?
Not necessarily, and a midgame lead in stones is often bad news. Only the final count decides the game, and any lead along the way can be undone by a single move. Holding more stones usually means more of them are exposed in more directions, which gives your opponent more legal moves rather than fewer. The Normal computer here scores by stone count, so it always takes the most stones available, which is also where it is easiest to beat; try the same mobility play against Strong and see how much harder it gets.
Why do the corners matter so much in Reversi?
Flipping requires stones on both ends of a line, and a corner has no far side in any direction, so a stone in a corner can never be flipped back. It also becomes a fixed anchor for the edge and the diagonal running from it, which gradually makes neighboring stones safe as well. The squares immediately next to a corner do the opposite: playing them usually hands the corner to your opponent.
Can I turn off the legal move hints?
Yes. The Show legal moves switch in the lobby is on by default and highlights every playable square; during a game the eye button in the top bar toggles it too. Legal moves in Reversi are often unintuitive, so the hint saves you from guessing square by square. Once you no longer need it, turn it off: reading the board is part of the game.