If there’s no headers or obvious tells at a framework level, it can be hard to detect server-side code. Maybe Ruby-specific serialization in session cookies, or

If there’s no headers or obvious tells at a framework level, it can be hard to detect server-side code. Maybe Ruby-specific serialization in session cookies, or the name of session cookies, use of HTML templates or code gen or URL patterns... but there can be tons of false positives. Client-side is much easier and a whole different story. Same with pre-built client code like CSS in WordPress templates, or standard admin login pages.