Rails 5.2 supports HTTP/2 Early Hints for faster pages

Rails 5.2 includes support for HTTP/2 Early Hints, an optimization technique that allows the server to send preload instructions to the browser before the full response is ready.

What are Early Hints?

With HTTP/2, servers can send a status code 103 Early Hints to suggest which assets the browser should start preloading. This can improve perceived performance by beginning asset fetching early.

How it works in Rails

If you're using a server that supports Early Hints (like Puma + NGINX with proper configuration), Rails 5.2 can automatically send headers like:

1Link: </stylesheets/application.css>; rel=preload; as=style

This happens while the server is still rendering the page.

Enable it

Early Hints are sent automatically when:

• The app is running in production
• The web server supports forwarding 103 headers
• config.public_file_server.headers is properly configured

To start the server with Early Hints enabled pass --early-hints like this:

1bin/rails server --early-hints

Links

• PR #30744 - Adds HTTP/2 Early Hints for Rails
• Documentation for HTTP/2 Early Hints

Summary

Early Hints is a performance enhancement that takes advantage of modern browser capabilities and HTTP/2 features. Rails 5.2 makes this cutting-edge optimization available with minimal setup.