I'm working on One Simulator (
https://onesimulator.slidingcodes.com), a One Piece TCG simulator that runs entirely in the browser: online
matchmaking, spectating, ranked, deck builder, replays (and alt cards you can flex on your opponent).
Playing this game online used to mean installing something first: a client on
your PC, an app sideloaded onto your iPhone, or a tabletop sandbox where you
apply the rules yourself. And your opponent had to do the same before you could
play. Now you open a link and you're in a match, on any device.
The hard part turned out to be the rulings, not the netcode. I play this game in
real life and I still had to look half of these interactions up, because what a
card says and what a card does are two different documents. New sets land almost
every month, and every one of them is a pile of new special cases to implement
and test by hand. Which is why I now spend a suspicious amount of time wondering
whether I should just train an agent to do it instead of me.