Othello

Rules

Place a disc to outflank your opponent: your disc must form a straight line (horizontal, vertical, or diagonal) with another of your discs, with one or more opponent discs in between. All outflanked discs flip to your color. If you can't make a valid move, your turn is skipped. The game ends when neither player can move. Most discs wins.

The AI: Minimax with Alpha-Beta Pruning

The AI looks 5 moves ahead using a tree search. At each level, it assumes Black picks the move that maximizes the score and White picks the move that minimizes it (minimax). Alpha-beta pruning skips branches that can't possibly affect the outcome, cutting the search from ~30,000 nodes to ~3,000.

Board Evaluation (Heuristic)

The AI scores positions using: corners (worth +25, nearly uncapturable), edges (+5, stable), squares adjacent to corners (-10, dangerous to occupy early), mobility (how many moves you have vs opponent), and disc count (only matters late-game). This weighted sum guides the search.

About Othello

Othello (also called Reversi) is a two-player abstract strategy game on an 8×8 board. Each side has 64 disks white-on-one-side and black-on-the-other. Players alternate placing disks; any disks flanked between two of your color flip to your color. Whoever has the most disks of their color when the board fills wins.

How to play

Each turn, place one disk on any empty square that flanks at least one enemy disk (in any direction — horizontal, vertical, or diagonal) between your new disk and another of your existing disks. All flanked enemies flip. If you have no legal placement, you pass. Game ends when neither side can move.

Frequently asked questions

How is Othello different from chess?

Othello takes minutes to learn; chess years. Othello games typically end in 60 moves; chess can stretch hundreds. Othello also features the famous "mobility paradox" — having many pieces early is often a disadvantage.

Best Othello opening strategy?

Counterintuitively, prefer to have FEWER disks early. More disks reduce your move options and give opponent more flanking targets. Aim for "quiet" central play; corners and edges become decisive in the endgame.

Is Othello solved?

8×8 Othello is not yet weakly solved (as of 2026), but engines play above all-time human champion level. 6×6 was weakly solved in 1993 (draw with perfect play).

What's the corner strategy?

Corners are permanent (can never be flipped). Avoid giving your opponent access to a corner; squares adjacent to corners ("X-squares") often hand the corner to opponent if you play them early.

Related games

Chess — two-player abstract strategy.
Go — territory and influence.
Backgammon — dice race classic.
Mancala — ancient count-and-capture.