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Reversi

Classic Othello — flip discs to dominate the 8×8 board vs AI.

Plays in browser⌨️Mouse click⏱️5–20 minMedium
Score0
2
vs
2
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Reversi

You play as Black. Flank White discs to flip them. Most discs at the end wins.

Difficulty
Click a highlighted square to place your disc

How to Play Reversi

  1. Click an empty cell to place your disc — you can only play in a cell where your move flips at least one opponent disc.
  2. All opponent discs sandwiched between your new disc and your existing ones flip to your colour instantly.
  3. The player with the most discs on the board when it is full wins the game.
  4. If you have no valid moves on your turn, your turn is automatically skipped and play passes to your opponent.

About Reversi

Reversi (marketed as Othello by Mattel) is one of the most strategically deep two-player board games ever devised. Despite simple rules — place a disc, flip opponent discs — the game tree rivals chess in complexity. Three AI difficulty levels are available: Beginner uses random valid moves, Intermediate uses a greedy strategy maximising flips per move, and Expert applies minimax with alpha-beta pruning and positional weight tables that prioritise corners and edges.

Corner control is the fundamental strategic insight: corners cannot be flipped and anchor large stable regions. Mastering when to sacrifice short-term disc count to secure corners separates casual players from strong ones. Free in your browser, no download required.

Frequently Asked Questions

Why are corners so important in Reversi?
Corner discs can never be flipped once placed, making them permanently yours. They also anchor large stable regions — chains of adjacent discs that become equally unflippable — which gives corner control a compounding strategic advantage.
What is the minimax algorithm used in Expert mode?
Minimax is a search algorithm that evaluates all possible move sequences several turns ahead, choosing the move that maximises your score while assuming your opponent always plays optimally. Alpha-beta pruning makes this efficient by skipping branches that cannot improve on already-found moves.
How long does a game take?
A typical game lasts 5–15 minutes depending on the AI difficulty level and how long you take to consider each move.
Can I play against another human?
The game currently supports single-player mode against the AI. Human-vs-human on the same device may be added in a future update.