a simple, api for the fast lookup of usernames based on a web address, or vice versa

An example

creator.io constructs a tweet for you from the RSS feeds you follow so you can curate content on your own feeds and blogs. You want to mention the feed owner, but you don't know their twitter username, neither does creator.io, until now.

creator.io ⇢ W? API

PHP curl request to 
"https://whosername.com/api/[api_key]/bbc.co.uk/json

W? API ⇠ @bbcnews

Having received the username from the W? API, creator.io can now send the tweet with the BBC username.

BBC News - Ukraine and pro-Russia rebels sign ceasefire deal http://bbc.in/1rFdHmn via @BBCNews

Because automation is better.