What is ssr-rs?

ssr-rs lets a backend written in Rust render JavaScript web apps into ready-to-send HTML. Normally, if you want server-side rendering (SSR) for a React or Svelte app, you'd need a Node.js server running alongside your backend. This project eliminates that extra piece, your Rust server reads the pre-built JavaScript bundle and produces the final HTML string directly. Under the hood, it embeds V8 (the same JavaScript engine that powers Chrome) directly inside the Rust process. You load your bundled JavaScript file, point it at the right entry point (the function that generates the HTML), and call a render method. You can also pass in data as JSON, like route parameters or user info, which your JavaScript code can use to produce the right page content. The result comes back as an HTML string you can return from any web framework. The primary audience is developers building web apps with a Rust backend who want the SEO and performance benefits of server-side rendering without maintaining a separate Node.js service. For example, if you're running an Actix-based API and want to serve a React 18 frontend with initial HTML already rendered, this handles that. It currently works with bundles produced by Vite, Webpack, and Rspack, and supports React 18 and Svelte 4. One notable design choice is around threading. Even though V8 technically supports accessing a single instance from multiple threads, this crate deliberately forbids it, partly due to limitations in the underlying Rust bindings, and partly because rendering HTML doesn't really need shared state. Instead, each thread gets its own instance, which keeps things simpler and avoids potential crashes. This project also serves as the foundation for Tuono, a fullstack React framework built around Rust and SSR. The maintainer has flagged future exploration into V8 snapshots and WebAssembly-based JavaScript compilation, suggesting the project is still evolving.