Ruby on Rails: Application framework

What Ruby on Rails is

Rails is a Ruby web framework that renders server-side. It exposes per-request processing time in a response header and names its session cookie after the application, which together make it identifiable without any framework banner.

How DNSTrace.dev detects it

Detection reads the final HTTPS response and the first bytes of its markup. One matching signal is reported as strong evidence; two or more independent signals are reported as confirmed.

x-runtime — The time Rails spent processing the request, emitted by default middleware.
A session cookie matching _<app>_session — The Rails naming convention for the application session cookie.
server: Puma — The default Rails application server, reported as the runtime rather than the framework.

What a detection proves

The response was produced by a Rails application.

What it does not prove

The Rails version or the hosting platform. The x-runtime header is sometimes stripped at a proxy, and the session cookie name can be changed.

Common questions

Is x-runtime unique to Rails?

It is strongly associated with Rails middleware but not formally reserved, which is why DNSTrace.dev prefers to see the session cookie pattern alongside it before reporting the detection as confirmed.

Does Puma prove Rails?

No. Puma serves other Ruby frameworks too, so it is reported as an application runtime on its own.