[drdaeman]

Fails to parse http://io/ as valid URL. Same with IDNs, http://пример.испытание/. Okay, that's obscure cases, but when you're writing yet another link shortener you really should know quite a bit about URIs (and IRIs).

Practical problem is, service does not make distinction between http and https schemes - typing in https://example.org/ yields http://www.donotlink.com/ZG which leads to http://example.org/.