Reversi is a strategy game for two players on an 8×8 board with 64 discs that are black on one side and white on the other. The game starts with four discs in the center. On each turn a player places a disc of their color so that it outflanks at least one straight line of the opponent’s discs, and every outflanked disc is flipped to the mover’s color. A player who cannot make such a move passes. When neither player can move, the player with the most discs on the board wins. This guide explains every rule in detail, including the ones that cause arguments, and states exactly which version this site plays.
Watch: how to play Reversi
How to Play Reversi: Rules Explained Simply
Chapters
Overview
| Feature | Details |
|---|---|
| Players | 2 (or 1 against the computer) |
| Typical time | 10 to 20 minutes per game |
| Ages | About 7 and up |
| Equipment | An 8×8 board and 64 two-colored discs |
| Moves per game | At most 60, one for each empty square at the start |
The rules fit on an index card, yet the game rewards deep planning, because a single move can flip discs in several directions and change the look of the whole board. That combination of simple rules and long-term strategy is why Reversi has stayed popular for well over a century, and why it became one of the classic test problems for computer game-playing programs.
A short history
Reversi comes from England in the 1880s. Two men, Lewis Waterman and John W. Mollett, both claimed to have invented it, and early sets appeared under several names. In the original game the players placed the first four discs themselves in the four center squares, so a game could start from different patterns.
In the 1970s a commercial version published in Japan fixed the opening position, with the two pairs always placed diagonally. That modern form is the one played almost everywhere today, including in tournaments, and it is the version described in this guide and played on this site.
Setting up
Place the board between the players. Each player takes a color: one plays Black (the dark side of the discs) and the other plays White. Then put four discs in the center squares in a diagonal pattern:
- White discs go on d4 and e5.
- Black discs go on e4 and d5.
- The other 60 squares are empty.
Squares are named like a map: the columns are letters a to h from left to right and the rows are numbers 1 to 8 from top to bottom, so a1 is the top left corner. The four squares the discs start on are the center of the board, and the 4×4 block of 16 squares that contains them (c3 to f6) is often called the “sweet sixteen”.
Objective
Have more discs of your color on the board than your opponent when the game ends. It does not matter how many discs you have during the game. Positions change so quickly that a player with only a handful of discs in the middle game can still win by a wide margin.
How a turn works
- Black moves first. After that the players alternate.
- On your turn, place one disc, your color facing up, on an empty square.
- The square must outflank at least one line of your opponent’s discs (see below).
- Flip every outflanked disc to your color.
- It is now your opponent’s turn.
If you have no square that outflanks anything, you pass and your opponent moves again. You can never pass while a legal move exists.
The rules in detail
Outflanking
A line of discs is outflanked when it is a straight, unbroken row of one or more of your opponent’s discs with your newly placed disc at one end and another disc of yours at the other end. For example, if White has discs on c4 and d4 and Black has a disc on e4, Black can play b4: the two white discs are trapped between b4 and e4 and both turn black.
The line must be continuous. An empty square anywhere in the line breaks it, and so does one of your own discs: the run of opponent discs stops at the first disc of yours. Only the opponent discs up to that point flip.
Lines in all eight directions
From the square you play, lines can run in eight directions: left, right, up, down and the four diagonals. A single disc may outflank lines in several directions at once. Lines never wrap around the edge of the board.
Every outflanked line flips
When your move outflanks more than one line, all of them flip. You cannot choose to flip only some lines, and you cannot leave out discs in a line you outflank. In a physical game, flip them all before your opponent moves; if you forget one, the usual courtesy is to correct it as soon as someone notices.
No chain reactions
Only the disc you just placed can outflank. Discs that were flipped during your move do not outflank anything themselves, even if they now appear to trap another line of your opponent’s discs. Those discs stay as they are until a later move outflanks them.
Every move must flip at least one disc
You may not place a disc on a square that outflanks nothing, even if it is next to other discs. This is the rule that decides where you are allowed to play, and it is why the number of available moves, called mobility, is such an important part of strategy. On this site, dots mark every square where the player to move can play (you can switch these hints off in the More menu).
Passing when you cannot move
If you have no legal move, you must pass and your opponent plays again. If they still have moves, they keep playing until you have a legal move again. Passing is not optional: you cannot pass to avoid a bad move, and you must play if any legal move exists. On this site the game plays a forced pass for you and a short message tells both players who had to pass. With the optional pass screen on, a pass doesn’t bring the screen up: the device stays with the player who moves again.
Running out of discs
A physical set has 64 discs, one for every square, split between the players: 32 each. If a player runs out of discs but still has a legal move, the opponent hands them a disc to play. On this site there is no supply to run out of, so a player with a legal move can always play it.
When the game ends
The game is over as soon as neither player can move. Usually that is because all 64 squares are full, but it also happens when one color has been completely wiped out, or when the last empty squares cannot be reached by either player. There is no need to pass twice: once neither side has a legal move, the game ends and the discs are counted.
Winning, drawing and counting
When the game ends, each player counts the discs of their color on the board. The player with more discs wins. If both have the same number, the game is a draw. On a full board that means 32 discs each.
This site counts discs only, so a game that ends early with empty squares is scored exactly as it stands, for example 40–21. In official tournament play the empty squares are added to the winner’s total, which would make that result 43–21. The winner is the same either way; only the margin changes. Because games are fairly short, many people play a series and alternate colors. The game-over screen here keeps a running score for your session.
Variants and which one this site uses
This site plays the standard modern rules described above: an 8×8 board, the diagonal starting position, Black moves first, forced passes, the game ends when neither player can move, and the most discs wins. Rematch swaps colors so both players get turns at moving first. Other versions you may come across:
- The original opening. In the 19th-century game the board started empty and the players placed the first four discs in the center squares themselves. Starting side by side instead of diagonally changes the early game noticeably.
- Other board sizes. A 6×6 board makes a quick game that is good for learning, while 10×10 boards give longer, more strategic games. The rules are the same.
- Anti-reversi. Also called reverse or misère play: the player with the fewest discs at the end wins. It turns normal strategy upside down.
- Handicap games. A stronger player gives a weaker one a head start, for example by letting them start with an extra disc in a corner.
- Timed games. Tournament players use a clock with a fixed amount of thinking time per player for the whole game.
Common mistakes and rule disputes
“I can play anywhere next to a disc.” You can’t. A move is legal only if it flips at least one disc.
“Only one line flips.” Every line the new disc outflanks flips, in every direction at once.
“My flipped disc traps another line, so that flips too.” No. Only the placed disc outflanks; there are no chain reactions.
“I’ll pass this turn.” You may only pass when you have no legal move at all.
“The game is over because I can’t move.” Not if your opponent can still move. They keep playing until you have a move again or nobody can move.
Missing a line when flipping. In a physical game it is easy to overlook a diagonal. Check all eight directions from the square you played. On this site the flips are done for you.
Thinking the player ahead in the middle game is winning. Disc counts swing wildly, and a big lead early on often means fewer moves to choose from later. The count only matters at the end.
Glossary
- Disc: a playing piece, black on one side and white on the other.
- Outflank: to trap a straight line of opponent discs between the disc you place and another of your own.
- Flip: to turn an outflanked disc over to your color.
- Legal move: a square where placing a disc outflanks at least one line.
- Pass: to give up your turn because you have no legal move.
- Mobility: the number of legal moves a player has.
- Corner: one of the four corner squares (a1, h1, a8, h8). A disc there can never be flipped.
- X-square: a square diagonally next to a corner (b2, g2, b7, g7).
- C-square: an edge square right next to a corner, such as b1 or a2.
- Edge: the outer rows and columns of the board.
- Frontier disc: a disc next to at least one empty square.
- Stable disc: a disc that can no longer be flipped, such as a corner disc.
- Wipeout: a game that ends because one player has no discs left.
- Parity: who gets the last move, overall or in a small region of empty squares at the end of the game.
Play it now
The best way to learn the rules is a quick game. Open Reversi to play with a friend on one device or against the computer on Easy, Medium or Hard. When you know the rules, the Reversi strategy tutorial explains corners, mobility and parity, and plays through a first game step by step.
