Is there something like https://rubydoc.info/gems/mechanize/Mechanize for kotlin?

This looks like it’s related to UI. You would need to use XCUITest for SwiftUI/UIKit on iOS or Espresso for Compose on Android. Compose on desktop seems to also have a Espresso-like testing framework.

Close, but no cigar. It's to interact with websites based on HTML only. I don't think it does Javascript.

Are you building a site with Kotlin/JS, or asking about an equivalent on other platforms?

I'm asking for a library to interact with websites based on their HTML.

I’m not aware of anythin in Kotlin, but you might be able to make that library work by running it through JRuby or GraalVM, both of which are Java projects and should interop with Kotlin very well. Alternatively, you could probably write a lot of that functionality yourself on top of jsoup, which is a Java HTML parser. It makes it really easy to read and manipulate HTML documents

Kinda? https://github.com/GistLabs/mechanize