THE ARCADE / GUIDEBOOKOpen game

Reversi — guidebook

You play black against a white computer opponent. Place a disc to trap white discs in a straight line between your new disc and a black disc already on the board. Every trapped line flips to your colour. The player with more discs at the end wins.

The opening

The eight-by-eight board starts with four discs in its centre. Black moves first. Amber dots show your legal choices. Select one to place a disc; the computer replies after a short delay. The scores count the discs currently on the board, and the status explains turns, moves and passes.

The early score is not a prediction of the winner. A player can trail for much of the game and take control near the end.

A move must trap at least one uninterrupted line of opposing discs. Lines may be horizontal, vertical or diagonal. There must be at least one white disc between your new black disc and another black disc. An empty square breaks a line; the board edges do not wrap around.

For example, imagine an empty square followed by two white discs and then a black disc in one row. Placing black in the empty square flips both whites. If the same new disc also brackets a diagonal line, that entire line flips too. All qualifying lines are resolved together.

You cannot place on an occupied square or on an empty square that captures nothing. Selecting an illegal square leaves the board unchanged and asks you to choose an amber dot.

Passes and the end

If a player has no legal move, the game automatically passes that turn. You cannot choose to pass when a legal move exists. Sometimes the other side will therefore play twice or more in succession.

The game ends when neither side can move. This may happen before every square is filled. Only discs count: empty squares are not awarded to anyone. More black discs means you win, more white means the computer wins, and equal counts mean a draw.

Choose an opponent

Casual prefers corners and immediate captures, choosing randomly between equally attractive moves. It is a useful place to learn the board.

Thoughtful searches three moves ahead and also values mobility, corners and the danger of playing beside an empty corner. It is stronger, but is not presented as tournament-level AI. Changing strength replaces the current game, with confirmation after play has started.

Controls and reading the board

Tap or click an amber-dotted square. With the board focused, use arrow keys to move the cell focus and Enter or Space to play. Tab reaches the opponent selector, New game and other controls.

An amber ring identifies the last white move, which helps you follow the computer's reply. Disc changes animate briefly unless reduced motion is requested by your device/browser. The board fits a narrow screen; scroll for the instructions below it.

There is no pause button. The game waits on your turn. A pending computer turn completes after its short delay, then it waits again unless you must pass.

A practical playbook

  1. Watch the corners. A corner disc cannot be flipped. Think carefully before giving the opponent a move there.
  2. Be cautious beside empty corners. The adjacent edge and diagonal squares can offer the opponent a route into that corner.
  3. Keep choices available. Having several legal moves gives you flexibility. A move that flips fewer discs now may leave a better position.
  4. Look at the reply. Before moving, consider which legal squares the new board will give white.
  5. Count near the end. With few empty squares left, direct disc gains and forced passes become much more important.

These are useful habits, not guarantees. Edge squares are not all permanently safe, and the largest immediate capture is not always the best move.

Results, replay and saves

The result appears as soon as neither side can move. The counts remain visible. New game starts again at the selected strength. During an unfinished match, New game asks before replacing it; Keep playing or Escape dismisses that confirmation.

This edition has no Undo, saved matches, accounts or multiplayer. Reloading starts a fresh board. Opening the full guidebook uses a separate tab, keeping your current game open.

Install and offline play

Load the complete standalone game online once. Install uses your browser's Install app or Add to Home Screen flow if available. On iPhone/iPad Safari, use Share then Add to Home Screen. Installation is optional; browser play works without it. After that first complete online load, the game and this guidebook work offline. An embedded game leaves installation to its host site.

Use your browser's Print command to print the guidebook or save a PDF. Physical-phone installation and performance have not been verified on a device.

Troubleshooting

If there are no amber dots, it may be the computer's turn or the game may have ended. A pass message explains any forced skipped turn. An empty square without a dot is not a legal black move.

If a line did not flip, check whether it was uninterrupted and ended at your existing disc. If offline loading stops after browser data was cleared, load the standalone page online again.