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Topcoat enables Rust to render server-side web apps

Software1 min read

Topcoat is a new Rust framework that builds web apps mostly on the server, not in the browser. Its creator, Carl Lerche, says this could make pages load faster.

What happened

At a virtual conference, Amazon Web Services engineer Carl Lerche showed Topcoat. It is a framework for building web apps in Rust, a programming language usually used for other jobs. Topcoat turns Rust code into JavaScript, which web browsers understand.

Key facts

  • Lerche is best known for creating Tokio, a popular tool for running Rust code that does many tasks at once.
  • Lerche says Topcoat is not for very complex apps, but it fits the typical database-driven web apps that make up about 90 percent of the web.
  • Topcoat renders all page components at once, instead of one by one, to save loading time.
  • The talk was given at ScyllaDB's 2026 P99 virtual conference.

Why server-side pages are back

Many modern web apps run most of their logic in the browser. Topcoat takes a different path. Most of the logic runs on the server, and only the results are sent to the browser. When a user clicks a button, only the small piece of the page that changed is sent back and refreshed. Other tools, such as HTMX, Datastar, and Phoenix LiveView, use similar ideas.

Why it matters

Rust is known for speed and safety, so some developers may want to use it for web work. Other Rust web tools, like Leptos and Dioxus, run Rust in the browser through WebAssembly, which can be slow to load. Topcoat tries to avoid that delay. Still, it is a new project, and its real speed and fit for big projects are not yet proven.

What to watch

  • Whether developers adopt Topcoat for everyday web apps.
  • How fast Topcoat pages load compared with other frameworks.
  • How well Topcoat works for large, complex apps.

Glossary

Topcoat
A new framework for building web apps in Rust, with most logic run on the server.
Rust
A programming language known for speed and safety.
Tokio
A popular tool that helps Rust programs run many tasks at the same time.
Amazon Web Services
A cloud company whose services let businesses run computers and software online.
WebAssembly
A format that lets code run in a web browser at high speed, often used for heavy tasks.

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