Question: "should this be a server etc? (vs static HTML Server what is best)."
The entire InstaCalc Arcade is designed as a 100% zero-backend client-side computing architecture. Here is why this delivers the highest performance and best developer/player experience:
InstaCalc's core math evaluator (/vendor/instacalc/engine/index.mjs) is pure modern JavaScript ESM. It compiles and evaluates mathematical formula DAGs directly in the browser's V8 engine in microseconds—eliminating the latency and cost of server roundtrips.
Because games and the arcade run in the same origin, the Arcade can inject modified .ic sheets and evaluated parameters directly into the running game's memory space using postMessage and direct runtime DOM bridges. Modifying a weapon stat or sprite updates the running game instantly at 60 FPS.
A static HTML server (e.g., Vite, python -m http.server, GitHub Pages, Cloudflare Pages, Netlify, or AWS S3) requires no database, no Node/Python backend maintenance, and no server security vulnerabilities. Anyone can clone the repo and immediately play or host it anywhere.
Everything runs safely sandboxed within browser security boundaries with complete offline capability.