Every string without a period is parsed by addressable

[sporkmonger]

Every string without a period is parsed by addressable

[sporkmonger]

That's not Addressable. That's the URI implementation in the standard library. Load Addressable with:

require 'addressable/uri'
Addressable::URI.parse(uri_string)

However, Addressable does not verify domain names. Domain names are not part of the URI spec, so Addressable intentionally does not verify them. The URI implementation in the standard library partially validates them, but there are plenty of valid domains that it rejects and plenty of invalid ones that it misses, so I don't recommend using it for this purpose.

RFC 1123 covers the hostname format.

This question on StackOverflow is similar to what you seem to be looking for.

If you need to verify more than just whether the URI is valid, I'd recommend checking out the Google Site Verification API.

[sporkmonger]

Also, I should add that the strings you're entering are in fact relative URIs, not domain names as far as the parse methods of both Addressable and the standard library are concerned. So yes, these will all be parsed without error, and that is 100% the correct result.