The game is by

Nazmi Elyigit

The rules are the original part, and they are unlike anything else in the trick-taking family. You must beat the best card of the led suit if you can. You must trump when you are void. You must beat a trump already on the table. There is no exception for your partner — if the only card that takes the trick is yours, you take it off them. And the contract is settled long before the cards run out — trick three is ordinary — but the hand is played out to all nine, because the tricks after that are the score.

That combination is what makes the game worth building software for. The forcing rules cut the branching factor so far down that the game can be solved exactly, so this app can tell you not just what you played but what was actually available. None of that is a property of the code. It falls out of the design.

The engine, the solver, the AI and these apps are an implementation. The game is not.

The app

A rules engine, an exact double-dummy solver, and an AI that bids from a model trained on solved deals. The same TypeScript runs in the browser, on the server and on iOS, which is why a finished hand can be reviewed card by card with exact numbers rather than estimates.