Reversi has few rules, but beginners tend to stumble over the same points: not every empty square is legal, one move may flip in several directions, and the board need not be full when the game ends. The sections below follow the checks you make on each turn, from legal moves and flips to passes and the final count. After reading, open an AI game, find a dotted square, and trace the bracketed discs along each line.
The board and the four starting discs
The board is 8×8. Four discs are already placed in the center: White on d4 and e5, Black on e4 and d5. Black moves first. Players then take turns placing one new disc on an empty square. A disc is never moved to another square; it changes only when a later move flips it.
Letters above the board name the columns, and numbers along the side name the rows, so d3 is where column d meets row 3. You do not need to memorise coordinates to play. They simply make it easier to identify a move during a replay.
Play the first move step by step: Black to d3
At the start, Black has four legal moves: d3, c4, f5, and e6. The board marks them with dots. We will use d3 below, but any of the other three dotted squares is also legal.
- Confirm that the destination is empty. There was no disc on d3.
- Look outward in all eight directions. Downward from d3, the first disc is White on d4, followed by Black on d5.
- Find a closed line of opposing discs followed by one of your own. That bracket makes d3 a legal move.
- Flip only the opposing discs inside each closed line. Here d4 flips; no other direction forms a bracket.
If you understand why d4 flips, you understand the core rule. However crowded the board becomes, you still begin at the square you played and check the same eight directions one by one.
What makes a move legal
From the empty square you choose, inspect all eight directions: two horizontal, two vertical, and four diagonal. A direction qualifies when you first meet one or more consecutive opposing discs and then one of your own. Every opposing disc between the new disc and your existing disc flips.
If the square brackets no line in any direction, the move is illegal. This board marks legal squares with a small dot; tapping an unmarked square will not place a disc.
Check a bracketed line with one move
Suppose you are Black and a row reads, from left to right: an empty square where you intend to play, White, White, Black. When you place a black disc on the empty square, the two white discs are bracketed by the new black disc and the existing black disc, so both flip. Without the black disc at the far end, the line would remain open and could not make the move legal.
One move may close several lines at once. Do not stop after noticing the most obvious row. Check the column and both diagonals as well; every direction containing consecutive opposing discs followed by one of your own flips together.
When you have to pass
If no square is a legal move on your turn, you must pass and give the turn to your opponent. If they have a legal move, play continues; if they do not, the game ends. You may not choose to pass while a legal move exists.
How to count the final position
When neither side has a legal move, count the black and white discs on the board. The side with more discs wins; equal counts produce a draw. Empty squares score nothing. AI and shared-device games support undo and replay, while a move synced in an online room cannot be withdrawn by one player.
The board does not have to be full. If Black has no legal move and White also has none, the game ends immediately. Conversely, if either side can still move, play continues even after the other side has just passed.
Questions people ask before the first game
Is this the same game as draughts or checkers?
No. Draughts slides and hops on dark squares. Reversi adds a disc to an empty square and flips the line it closes. The boards look square. The rules do not overlap.
Why will the board not accept the square I clicked?
That square does not bracket any opposing discs. Look for a dotted square. If there are no dots at all, press Pass.
Does the game have to fill all 64 squares?
No. As soon as neither side has a legal move, count the discs and end the game, even if empty squares remain.
Can one move flip horizontally, vertically, and diagonally at the same time?
Yes. Check all eight directions after placing the disc. Every direction that forms a closed line of the new disc, one or more consecutive opposing discs, and one of your existing discs will flip.
Can I choose to pass when I have a legal move?
No. Passing is not a strategic option; it is required only when you have no legal move. If the board still shows a dotted square, you must play on one of those squares.
