It works just like TinyURL and its ilk, accepting a URL and [having a crack at] shortening it. It checks both the response headers and (shortly) the HTML itself for rel=shortlink and if they're not present then you have the option of falling back to a traditional service (the top half a dozen are preconfigured or you can specify your own via the API's "fallback" parameter).
An interesting facet of this implementation is the warnings it gives if it encounters the similar-but-ambiguous short_url proposal and the fatal errors it throws up when it sniffs out the nothing-short-of-dangerous rev=canonical debacle. Apparently people (here's looking at you Ars Technica and Dopplr) felt there was no harm in implementing these "protocols". Now there most certainly is.
Here's the high level details (from the page itself):
WhoSo have at it and let me know what you think. The source code is available under the AGPL license for those who are curious as to how it works.
A community service by Sam Johnston (@samj / s...@samj.net) of Australian Online Solutions, loosely based on a relatively good (albeit poorly executed) idea by some some web developers purporting to "save the Internet" while actually hurting it.
A mechanism for webmasters to indicate the preferred short URL(s) for a given resource, thereby avoiding the need to consult a potentially insecure/unreliable third-party for same. Resulting URLs reveal useful information about the source (domain) and subject (path):
The shortlink Google Code project, the rel-shortlink Google App Engine application, the #shortlink Twitter hashtag and coming soon to a client or site near you.
Starting April 2009, pending ongoing discussion in the Internet standards community (in the mean time you can also use
http://purl.org/net/shortlinkin place of
Short URLs are useful both for space constrained channels (such as SMS and Twitter) and also for anywhere URLs need to be manually entered (e.g. when they are printed or spoken). Third-party shorteners can cause many problems, including link rot, performance problems, outages and privacy & security issues.
By way of
<link rel="shortlink">HTML elements and/or