How to Play Othello (Reversi): Rules, Passing and Scoring

To play Othello, two players take turns placing discs on an 8 by 8 board, and Black moves first. Every move must trap at least one of your opponent's discs in a straight line between the disc you place and a disc you already have, and every trapped disc flips to your color. If you can't make a move like that, you pass. The game ends when neither player can move, and the player with more discs wins.

Reversi is the older name for the same family of games, and Poozee's Reversi plays exactly the Othello rules below. Every diagram in this guide was checked with the game's own rules engine, and every number comes from games we had Poozee's computer players play. Once you know the rules, our Othello strategy guide covers how to win.

Othello rules at a glance

Squares are named by column and row: columns a to h from the left, and rows 1 to 8 counted from the top, the way Othello boards are labeled.

The starting position

Every game starts with the same four discs, crossed diagonally in the middle of the board. Black moves first:

Each of the four moves flips exactly one white disc, and the four positions they lead to are the same position turned or mirrored, so no first move is better than another. Say Black plays f5:

White can answer with d6, f4 or f6. After any of Black's four first moves, White has exactly three replies.

What counts as a legal move

A move is legal only if it flips something. To check a square:

1. It must be empty.
2. Look along each of the eight lines out from it: left, right, up, down and the four diagonals.
3. A line traps discs when it starts with one or more of your opponent's discs in a row and ends with one of your own. An empty square or the edge of the board before your own disc breaks the line.
4. If at least one line traps discs, the move is legal. Place your disc and flip every trapped disc in every one of those lines.

A few details settle most arguments:

• You flip all of them. You can't choose to leave a trapped disc unflipped, even when flipping it helps your opponent.
• No chain reactions. Only lines that run out from the disc you just placed are flipped. A disc that ends up between two of your discs some other way stays as it is.
• Discs never move. Once placed, a disc stays on its square for the rest of the game and can only be flipped.
• You can't pass while you have a legal move.

On Poozee, a dot marks every legal move on your turn, and the game flips the trapped discs for you. You can switch the dots off with Show legal moves if you'd rather find the moves yourself.

Flipping in several directions at once

One move often flips discs in more than one line. This position comes from the opening d3, c3, b3, e3, f3, f4:

Look out from f5 in each direction:

• Left: e5 is white and d5 is black, so e5 is trapped.
• Up: f4 is white and f3 is black, so f4 is trapped.
• Up and to the left: e4 is white and d3 is black, so e4 is trapped.
• The other five directions run into an empty square straight away.

So f5 flips three discs in three directions:

Look at d4. It sits between d3 and d5, and after the move it also sits between c3 and e5, yet it stays white. Neither line runs out from f5, so neither one counts. A single move can flip in as many as all eight directions, but only along lines that start at the new disc.

What happens if you can't move

If you have no legal move, you pass, and your opponent moves again. If you still have no move after that, you pass again, as many times as it takes. You can never pass by choice: as long as you have a legal move, you must play one.

This position comes from one of our games between two computer players:

White has 17 discs to Black's 14, but no move. From every empty square, each line that starts with black discs runs off the edge of the board before it reaches a white disc, so White has nothing to trap them against. White passes, and Black plays again.

Passes are common. In 1,000 games between two copies of Poozee's computer player, 506 had at least one pass, 960 passes in all. In 10,000 games between two players moving at random, 3,512 had a pass. Passes were more common between the computer players, which try to leave each other as few moves as possible; the strategy guide shows how to use that in the endgame.

On Poozee you never have to pass by hand. When a player has no move, the game says so ("The computer has no move and passes. Your turn again.") and the other player moves again.

How the game ends

The game is over when neither player can move. Most of the time that's because all 64 squares are full: the board starts with 4 discs, so a full game is 60 moves. In our 1,000 computer games, 924 filled the board, and the average game lasted 59.8 moves.

A game can also end with empty squares left, when neither player can flip anything from any of them. That happened in 76 of the 1,000 games, and in 56 of those exactly one square was left empty. Here's one:

After b7, every line from a8 runs through discs of one color all the way to the edge, so neither player can play there. Neither player can move anywhere else either, because a8 is the only empty square. The game ends with White ahead 32‑31, and White wins.

The shortest possible game

A game also ends when one player loses every disc: with no discs of your own, you can't trap anything, and your opponent then has nothing to flip. We had the computer play out every possible sequence of the first 9 moves, all 3,005,320 of them. No game can end in fewer than 9 moves, and 228 different nine-move games end with Black wiping out White. Here's the last move of one:

From f4, Black traps e4 to the left, e3 up and to the left, and e5 down and to the left. Wipeouts are rare in real games: 4 of our 1,000 computer games ended that way.

Counting the discs and ties

When the game ends, count the discs of each color. The player with more discs wins, and equal counts are a draw. On Poozee, empty squares don't count for anyone, and the result shows the two disc counts, like "It's a draw, 32‑32."

Draws are uncommon: 22 of our 1,000 computer games and 411 of the 10,000 random games were drawn, and every one of those 433 draws was 32‑32 on a full board.

In tournaments, the final score is counted a little differently. Under the World Othello Championship rules, empty squares are counted for the winner, and a draw is always recorded as 32‑32. The game above would go down as a 33‑31 win for White instead of 32‑31. The winner is the same either way; only the margin changes.

Poozee, tournament Othello and the original Reversi

Poozee plays the standard rules published by the World Othello Federation. Othello is a trademarked brand, and Poozee's Reversi isn't affiliated with it. The original Reversi was played differently: according to a World Othello Federation article on Reversi and Othello, it dates back to the 1880s, players took turns placing the first four discs in the center, and the game ended as soon as either player couldn't move.

The pass rule makes a big difference. Under the original Reversi rule, 506 of our 1,000 computer games would have ended at their first pass, often long before the board filled.

Playing on Poozee

• vs Computer: play Black (you move first) or White, on Easy, Medium, Hard or Expert. 2 Players lets two people share one screen.
• To move, tap or click a square with a dot, or Tab to the board, move with the arrow keys and press Enter.
• Undo takes back your last move, and Hint shows the move the Expert computer would play.
• Your game is saved in this browser, so you can close the tab and finish it later.

Keep playing

• Play Reversi against the computer or a friend
• Othello strategy: why corners and mobility beat grabbing discs, tested in thousands of games
• How to win at checkers, another classic board game we tested by computer self-play
• How to win Connect Four