Reversi

How to play Reversi

Black opens on the fixed 8 × 8 board. Place a disc on an empty square so that one or more opposing discs lie in a straight line between your new disc and an existing disc of your color. Every bracketed line flips to your color, including horizontal, vertical and diagonal directions. A legal move must flip at least one disc.

All captures are checked from the board before your move. You cannot jump over your own disc or an empty square, and newly flipped discs do not start extra chain reactions. The opening has two Black and two White discs in the center.

Passes and the final score

If the other side has no legal move, it passes automatically and you play again. You cannot pass voluntarily when a legal move exists. A side can sometimes make several consecutive placements. When neither side can move, the game ends, even if empty squares remain. A full board also ends the game.

The player with more actual discs wins; equal counts are a draw. Scores show the discs that are really on the board. Empty squares are not awarded to either player, and eliminating one color does not substitute a tournament 64–0 score.

Computer or two players

Choose Black to play first, or White to let the computer open as Black. Local Two players shares the same screen with Black first. Side and computer level controls apply only to computer games.

Easy varies its legal choices and prefers available corners. Normal uses short strategic lookahead. Hard and Expert use progressively larger, bounded searches that consider corners, mobility, exposed discs and the changing value of the endgame score. Forced passes are included in the search. These are site-specific strength settings, not a claim of optimal or unbeatable Reversi play.

Simple controls and legal dots

Tap a legal empty square. The light dots show legal placements, not strategic recommendations. The Legal moves button or L key toggles them without changing the rules or counting as assistance. Arrows explore the board; Home and End move across the current row, and Enter or Space attempts a legal placement on the focused square. U undoes, R redoes and P pauses.

During a computer turn, board input waits while New, Undo and Pause remain available when applicable. If you have to pass, the computer can play again automatically. Full screen keeps all 64 squares and the tools together; Back or Escape restores the page. Sound starts off, reduced motion is respected and star celebrations stay below the board.

Undo, saved games and practice

Against the computer, Undo returns to your previous decision, removing every computer placement and automatic pass that followed it. That can be more than two placements when you had to pass repeatedly. A final unanswered human move is undone alone. The automatic opening cannot be undone by itself. Local Undo removes one placement and rewinds the pass it caused. Redo restores the exact saved sequence rather than asking the computer for a different reply.

Your legal game history, derived turns and passes, Undo/Redo, active time, settings and achievements save in this browser when storage is available. Leaving the tab pauses and cancels pending computer work. A saved unfinished game waits for Resume before any reply. Old callbacks cannot change a replaced, paused, undone or completed game. A visible message explains when saving is unavailable.

Undo and Restart mark the same attempt as practice. Restart restores the opening but keeps the first outcome and assistance. Undoing a loss and later winning cannot turn the original loss into a fresh challenge win. New creates a fresh attempt. Reviewing, redoing, restarting and reloading do not duplicate a result.

Eight milestones

Earn stars for a first legal placement, placing a corner disc, flipping at least six discs in one move, finishing a first-result game, winning a first-result computer game, beating Hard or Expert without Undo or Restart, a computer win without Undo or Restart, and three different fresh computer wins. Local play can earn the opening, corner, capture and completion milestones; computer challenge stars require actual computer games. A temporary disc majority alone is not a victory.