Online Reversi

The classic strategy board game where you flip your opponent's disks to your color. Outflank, outthink, and outplay!

How to Play: Black always goes first. Players take turns placing disks on the board with their color facing up. A move consists of placing a disk on an empty square that outflanks one or more of the opponent's disks. Disks are outflanked when they are between two disks of the opposing color in a straight line (horizontal, vertical, or diagonal). All outflanked disks are flipped to the current player's color.

Two Players
vs Computer
2
Black Disks
2
White Disks
1
Turn
60
Disks Left
AI is thinking...
Black's Turn
White's Turn
00:00
Black: 2 - White: 2
Game Over!

Black wins with 32 disks to 32!

Move History

Moves: 5
1. Black: F4 (flips: 1)
2. White: D3 (flips: 1)
3. Black: C3 (flips: 1)
4. White: F3 (flips: 1)
5. Black: D6 (flips: 1)

About Reversi (Othello)

Reversi, also known as Othello, is a strategy board game for two players, played on an 8×8 uncheckered board. The game was invented in 1883 by either of two Englishmen (each claiming the other a fraud), Lewis Waterman or John W. Mollett. The modern version of the game, with the trade name Othello, was patented in 1971 by Goro Hasegawa.

Official Rules: The game begins with four disks placed in the middle of the board, two white and two black, with same-colored disks on a diagonal. Black always moves first. If a player cannot make a valid move, they must pass their turn. The game ends when neither player can make a valid move, usually when the board is full. The player with the most disks of their color wins.

Basic Strategy Tips

Control the Corners
Corners are the most valuable squares because they cannot be flipped once captured. Try to secure corner positions early in the game.
Avoid C-Squares
Avoid placing disks on squares adjacent to corners (C-squares) unless necessary, as this often gives your opponent access to the corner.
Mobility is Key
Try to maximize your own moves while limiting your opponent's options. Having more valid moves gives you flexibility.
Disk Parity
In the early and middle game, focus on position rather than disk count. Only in the endgame should you try to maximize disks.

Game Terminology

Term Definition Strategic Importance
Outflank Placing a disk so that opponent disks are between two of your disks Core game mechanic for capturing opponent disks
Stable Disk A disk that cannot be flipped for the rest of the game Corners and edges with proper support become stable
Mobility The number of legal moves available to a player High mobility gives strategic advantage and options
Frontier Disk A disk adjacent to an empty square Frontier disks are vulnerable to being flipped
Internal Disk A disk not adjacent to any empty square Internal disks are safer from being flipped
X-Square The square diagonally adjacent to a corner Dangerous square that often gives opponent the corner

Opening Strategies

1

Classic Opening: The most common opening moves aim to control the center while preparing for corner captures. Typical first moves are D3, C4, F5, or E6 (using algebraic notation).

2

Corner Grab: Some players use aggressive strategies to capture corners early, even at the cost of conceding many disks in the center. This can be risky but rewarding.

3

Balanced Approach: A balanced opening focuses on maintaining mobility and flexibility while avoiding premature commitments to any area of the board.

Frequently Asked Questions

Reversi is the original game invented in the 19th century. Othello is a trademarked version with fixed starting position (four disks in the center) and standardized rules. In common usage, the names are often used interchangeably, but technically Othello is a specific implementation of Reversi.

Reversi/Othello has been solved for some board sizes, but for the standard 8x8 board, the game has not been completely solved. However, computer programs have reached a level where they can consistently defeat even the best human players. For humans, the game offers deep strategic complexity with no single "perfect" strategy.

If a player has no legal moves on their turn, they must pass, and the opponent gets to play again. This can happen multiple times in a row. The game ends when neither player has any legal moves, which usually occurs when the board is completely full.

Corners are strategically important because once captured, they cannot be flipped. A disk in a corner is "stable" for the rest of the game. Additionally, corners allow players to control entire rows and columns, often leading to capturing many opponent disks. Most winning strategies involve controlling at least some of the corners.

The number of possible games is astronomically large. Estimates suggest there are approximately 10^28 possible legal positions in Othello. The game tree complexity is estimated at 10^58, making it far more complex than chess in terms of possible game variations.