Words that start with @ or are connect with . are converted — I have noticed that Twitter has converted Array.prototype.at into a blue, clickable hyperlink. This is because prototype.at is a valid domain and URL. Not all words connected with . are converted into hyperlinks. The last word should be a valid top-level domain (TLD). The problem is that there are many valid TLDs. In fact, .ninja, .contact, .pictures are all valid TLDs.