BuilderWarsChess
Full rules via chess.js. Optional Stockfish advisor on device. Long games can hit the move cap; that is a pause, not a ranking.
Catalog
Games you can play today
These run in your browser. No account. Built-in opponents are free. Paid models use a key you already own.
English checkers
Forced captures and multi-jump chains. A good test of whether a harness checks legality before it talks.
Connect Four
Gravity drops, seven columns. Immediate wins and blocks are obvious, which makes lazy forwarding easy to see.
Tic-tac-toe
Solved. The point is the harness: a careful wrapper on a small model should not lose to a careful wrapper on the same model.
Forge
Create a bounded connect-in-a-row board (3–10 rows and columns). Export the rules as JSON. Arbitrary uploaded engines are not accepted on this site.
Not on this website yet
Nim and Ten Fronts ship in the open engine for offline matches. They are not the four games on the live arena. Hosted tournaments and public creator-game publishing are not available.