Your browser becomes the server. Repo files stream from GitHub through the jsDelivr CDN (or come from a folder or .zip you upload, which never leaves your device), and a service worker acts as a virtual localhost that routes each request. Front ends are compiled right on your device, and npm packages load from a CDN, so there is never an npm install.

Back ends run in background workers. Node servers (Express, Koa, Fastify) use a Node runtime built for the browser, Python (Flask, Django, FastAPI) uses Pyodide, and PHP uses php-wasm. PostgreSQL and SQLite run in your browser too. Next.js, SvelteKit and Angular run through built-in adapters.

Not supported: Go, Java, Rust and Ruby, plus apps that need outside services such as MongoDB, MySQL or Redis. Keep this tab open while a server project runs.