About OthelloGame.app
OthelloGame.app is an independent, free website for playing Othello (also called Reversi) in the browser. The goal is simple: open the page and you are playing within a second, against a computer opponent that is easy to beat at first and very hard to beat at the top, with tools that help you improve.
Who writes the guides
The rules, strategy and history pages are written and maintained by the OthelloGame.app Editorial Team, the same people who built the game engine. Our standards:
- Rules are checked against the official text. Our rules page follows the World Othello Federation’s official rules, including tournament scoring.
- Every board diagram is computed, not drawn by hand. Diagrams that show a game are replayed through the same rules engine you play against, and the site will not build if a sequence is illegal.
- Strategy claims are tested. The ideas on the strategy page (corners, X-squares, mobility, frontier) are the same terms the computer opponent is scored on, and the level ladder is checked with automated matches.
- History is sourced and hedged. Where historical accounts disagree, for example who invented Reversi, we say so and link our sources.
- Corrections: found an error? Email contact@othellogame.app. We fix confirmed mistakes and update the date on the page.
How the computer opponent works
The engine is written from scratch for this site and runs entirely in your browser, in a background Web Worker:
- Rules engine: checked against the standard Othello move-count (“perft”) results from the start position up to 8 moves deep (390,216 positions), plus tests for passes, wipe-outs, scoring and undo.
- Search: negamax alpha-beta with iterative deepening and move ordering by corners and opponent mobility.
- Evaluation: corner ownership, X- and C-square danger (cancelled once the corner is taken), mobility, frontier discs, and disc count late in the game.
- Endgame: an exact solver takes over near the end: 14 empty squares on Strong, 16 on Master. From there it plays perfectly.
- Lower levels deliberately add randomness and search shallower, so they make human-like mistakes. In automated test matches each level beats the one below it.
The game review re-searches every position of your game six moves deep (exact from 14 empty squares) and compares your move with the best one. Scores are shown in discs.
Privacy
There are no accounts or ads. Optional Google Analytics runs only if you allow analytics cookies. Your settings, current game and win/loss record stay in your browser’s localStorage. Details are in the privacy policy and terms of use; to reach us, see the contact page.
Trademark notice
OTHELLO is a registered trademark of MegaHouse Corporation. OthelloGame.app is an independent site that teaches and hosts the public-domain game Reversi under the standard Othello rules; it is not affiliated with, sponsored or endorsed by MegaHouse or the World Othello Federation.
The board, discs, icons and all artwork on this site are original designs. We use the word “Othello” only to describe the game and its standard rules, the way players and the World Othello Federation do.
Accessibility
The board can be played with a keyboard: Tab to the board, arrow keys to move, Enter to place a disc. U undoes, H shows a hint and N starts a new game. Animations are reduced automatically if your system asks for reduced motion.
Last updated 2026-11-15.