How to Play Reversi
Reversi is a board game for two players that has been played for well over a hundred years. It has only one kind of move and one rule for it, so you can learn it in a few minutes, yet good players keep finding new ideas in it for a lifetime. The lead can swing back and forth right up to the last move, which is a big part of the fun. This page explains the rules step by step, exactly as our free online Reversi game plays them.
What You Need
- Players: two. Online, you play against the computer, or against a friend on the same tablet or computer.
- A board of 64 squares, eight across and eight down. All the squares are the same color; unlike a checkerboard, every square is used.
- Discs: 64 of them, each dark on one side and light on the other. One player plays dark, the other light. A disc is never removed from the board; it only changes color.
To make the moves easy to talk about, the columns are lettered A to H from left to right and the rows numbered 1 to 8 from top to bottom. So A1 is the top-left corner and H8 is the bottom-right corner. Our game prints these letters and numbers along the edges of the board.
The Aim of the Game
Have more discs of your color on the board than your opponent when the game ends. That is all. It does not matter how many discs you had along the way, and having a lot of them early on is often a bad sign, as the strategy guide explains.
Setting Up
The game starts with four discs on the four centre squares, set crosswise: light on D4 and E5, dark on E4 and D5. Each color is diagonal to its partner, making a little X in the middle of the board.
| D | E | |
|---|---|---|
| 4 | Light | Dark |
| 5 | Dark | Light |
Dark always moves first. Deciding who plays dark is up to the players. In our game you can choose in Settings: you go first, the other side goes first, or the game picks at random. See who goes first.
Making a Move
On your turn you place one disc of your color on an empty square. But not just any empty square will do. Your new disc must trap at least one of your opponent's discs.
A disc is trapped when it lies in a straight line between your new disc and another disc of your color that is already on the board, with no gaps and nothing but your opponent's discs in between. The line can run in any of eight directions:
- across (left or right),
- up or down, and
- diagonally (in any of the four diagonal directions).
Every trapped disc is then flipped over to your color. You flip all of them: you may not choose to flip only some. If your new disc traps lines in several directions at once, every one of those lines flips.
What does not count. An empty square in the line breaks it. The edge of the board breaks it. And a disc that is turned over during your move never sets off more flips; only lines that run out from the disc you just placed count. This is the rule people most often get wrong at home.
Worked example 1: the first move
At the start, dark has exactly four possible moves: D3, C4, F5 and E6. Take D3. Look down column D from D3: the next square, D4, holds a light disc, and the one after that, D5, holds a dark disc. So the light disc on D4 is trapped between dark's new disc on D3 and dark's disc on D5. It flips to dark.
After that move dark has four discs (D3, D4, D5, E4) and light has one (E5). Now it is light's turn, and light must find a square that traps one or more dark discs against E5.
Worked example 2: several lines at once
Later in a game, suppose you are dark and you place a disc on E5, and the board around it looks like this:
- To the left: light discs on D5, C5 and B5, then a dark disc on A5.
- Up and to the left (diagonally): light discs on D4 and C3, then a dark disc on B2.
- Below: a light disc on E6, then a dark disc on E7.
- To the right: a light disc on F5, then an empty square on G5.
Three lines are trapped: three discs to the left, two on the diagonal and one below. All six flip to dark. The light disc on F5 does not flip, because the empty square on G5 means there is no dark disc at the other end of that line.
Worked example 3: a square that is not allowed
Suppose you want to play next to a light disc, but beyond it there is only another light disc and then the edge of the board. Nothing is trapped, so the move is not legal, even though your disc would touch the other color. In our game such a square never shows a dot, and if you tap it anyway the game explains why it isn't allowed.
Passing
Sometimes a player has no legal move anywhere on the board. Then that player passes, and the other player moves again. A pass is not a choice: if you have even one legal move, you must play it, however little you like it. A player may pass several times in a row, and the other player keeps moving as long as they can.
In our game, passes happen automatically and are announced in a box above the board, for example "The computer has no move and passes. Your turn again."
The End of the Game
The game is over when neither player can move. Usually that is because all 64 squares are full, but it can happen earlier:
- when one player has no discs left at all (everything has been flipped to the other color), or
- when there are empty squares left, but neither player can trap anything by playing on them.
Counting and Winning
When the game ends, count the discs of each color. The player with more discs wins. If the counts are the same, the game is a tie. In our game the running count is always shown under the board, so there is nothing to count by hand.
| Final count (dark – light) | Result | Margin |
|---|---|---|
| 40 – 24 | Dark wins | 16 discs |
| 31 – 33 | Light wins | 2 discs |
| 32 – 32 | Tie | None |
| 0 – 13 (dark wiped out, 51 squares empty) | Light wins | 13 discs |
Some clubs give the empty squares of an unfinished board to the winner when they keep score over a series of games. That makes no difference to who wins a single game; see counting empty squares.
A Short Sample Opening
Here are the first four moves of a typical game, so you can follow along on the board.
- Dark plays D3, flipping D4. Count: dark 4, light 1.
- Light plays C3, trapping D4 diagonally against E5. Count: dark 3, light 3.
- Dark plays C4, trapping D4 across against E4. Count: dark 5, light 2.
- Light plays E3, which traps two lines at once: E4 down against E5, and D3 across against C3. Both flip. Count: dark 3, light 5.
Notice how the count swings back and forth. That keeps happening all game, which is why the count in the middle of the game tells you so little.
Rules People Often Ask About
Can I place a disc where it doesn't flip anything?
No. Every move must flip at least one disc. If you have no such move, you pass.
Can I choose which of the trapped discs to flip?
No. Every trapped disc in every direction flips.
Do discs flipped during my move flip others in turn?
No. Only lines running out from the disc you just placed count. There are no chain reactions.
Can I pass when I don't like any of my moves?
No. You pass only when you have no legal move at all.
Is a disc ever taken off the board?
Never. Discs only change color, so the number of discs on the board always grows by exactly one per move.
Is Reversi the same as the game sold under other names?
Several boxed games are based on Reversi with small changes, most often a fixed starting position. Our game uses the crossed start that most people know. Older Reversi rules let players place the first four discs themselves; the variations page describes that and other house rules.
Playing Online
In our game, squares where you can play are marked with a dot. Tap one and the discs that would flip are outlined; tap the same square again, or press Place Here, to play it. The Hint button suggests a move and tells you why, Undo takes back a move, and the Why? button beside each computer move explains its thinking. When you are comfortable with the rules, the strategy guide will help you win more. If you like board games against a fair computer, try Checkers too.