leptos-rs/leptos

Leptos is a framework for building web applications in Rust. Most web apps are written in JavaScript or TypeScript, Leptos lets you write the whole thing, the part that runs in the user's browser and the part that runs on the server, in Rust instead. Rust is known for being fast and for catching mistakes at compile time rather than after you ship, and Leptos uses WebAssembly (a way of running non-JavaScript code in the browser) to deliver that in a real web app. The framework is full-stack and isomorphic. Full-stack means it can render pages on the server, in the browser, or both (server-side rendering with hydration, where the server sends ready-to-display HTML and the browser then takes over for interactivity). Isomorphic refers to server functions: you write a function that talks to the database or handles authentication, and you can call it from your browser-side code as if it were local, without hand-building a separate REST API to glue the two halves together. Its main technical idea is fine-grained reactivity. Instead of re-rendering big chunks of the page when something changes (the virtual DOM approach used by some other frameworks), Leptos tracks individual reactive values called signals, when a signal changes, only the specific text, attribute, or element that depends on it is updated. The README claims this gives very low overhead. You describe the page declaratively with a view macro that looks a bit like HTML embedded in your Rust code. Leptos ships its own router, templating, and reactivity primitives, and recommends a companion build tool called cargo-leptos plus starter templates for the Actix and Axum web servers. Useful when you want to build interactive web apps in Rust end-to-end.