You can use shortr.at directly in your browser, too. There are many PlugIns for the popular browsers out there, which support custom shortening services. Just look for one which lets you change the URL query and enter the text snippet below.
http://shortr.at/api.php?signature="secret"&action=shorturl&format=simple&url=%URL%
Replace the "secret" in the URL above with your secret token. You can find your secret token by logging in and clicking on Tools. For Firefox we recommend Copy ShortURL 2.0.
If you are a developer and want to use our shortening service in your work, you can use our API. Have a look at YOURLS API Wiki and see how easy it is to use shortr.at API. Contact us to get a username, password and a secret token.