Reversi
Play Reversi against the computer or a friend, with move hints and undo.
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Reversi is a two player strategy game played on an eight by eight board with discs that are dark on one side and light on the other. The game starts with four discs in the centre, two of each colour placed diagonally, and dark moves first. On every turn you place a disc of your colour so that it traps one or more straight lines of your opponent's discs between the new disc and another disc you already own. Every trapped disc is flipped to your colour. Lines can run horizontally, vertically or diagonally, and a single move can flip several lines at once. When the board is full, or when neither player can move, the player with more discs wins.
Frequently asked questions
How do you play Reversi?
Is Reversi the same as Othello?
What happens when a player has no legal move?
How strong is the computer?
Why does having more discs early not mean I am winning?
Can I undo a move?
Is my game data sent anywhere?
Can I play with the keyboard?
About Reversi
The rules fit on a postcard, but the strategy is famously deep, which is why the game is often described with the phrase "a minute to learn, a lifetime to master". The number of discs you hold in the middle of the game means very little, because they can change colour many times. What matters is position and mobility. Corners can never be flipped, so a corner disc is permanent and often anchors whole edges. The squares diagonally next to an empty corner are dangerous, since playing there tends to hand the corner to your opponent. Strong players also try to keep their own number of legal moves high and their opponent's low, which often means taking fewer discs early rather than more.
This browser version follows the standard rules used in tournaments, including the pass rule: if you have no legal move you must pass, and the game ends when neither side can play. You can play against the computer at three levels. Easy grabs whatever flips the most discs right now, Medium judges squares with a positional weight table, and Hard runs an alpha-beta search several moves deep that values corners, mobility and edge stability, then switches to an exact search of the final moves. You can also play a local two player game on one device, choose which colour you take against the computer, show or hide legal move markers, and undo moves.
Everything runs in your browser, with no account and nothing to install, and your win tally is stored only on your device. The board works with a mouse, a touch screen or the keyboard: arrow keys move between squares and Enter places a disc. If you are new to the game, leave the legal move markers on, watch which squares the Hard engine fights for, and you will quickly start to see why the edges and corners decide most games.
Reversi: A Victorian Parlour Game That Became a Computer Science Benchmark
Reversi appeared in Victorian England in the 1880s, and two men, Lewis Waterman and John W. Mollett, each claimed to have invented it, with a public dispute over who came first. The early game used a cross shaped board in one version and let players place their first discs anywhere, and it was sold by the London publisher Jaques, the same company known for croquet sets. It was popular enough to be mentioned in newspapers of the time and sold under several names across Europe.
In the early 1970s a Japanese salesman, Goro Hasegawa, popularised a version with a fixed starting position of four diagonal discs and a green board, and marketed it under a trademarked brand name that drew on Shakespeare's play about jealousy and reversal of fortune. That standardised version became the basis of modern tournament play, and world championships have been held since 1977.
The game has also played an important role in artificial intelligence. Programs reached superhuman strength early: in 1997 the program Logistello, written by Michael Buro, beat the reigning human world champion six games to nothing. In 2023 researchers announced that the standard eight by eight game is a draw with perfect play by both sides, after a massive computer search, which places Reversi alongside checkers and connect four as one of the classic board games whose outcome under perfect play is now known.