I see that you found the Compete API. Let me begin by pointing you to the full
API documentation, which you can find at https://www.compete.com/developer/. I
recommend that you go ahead and take a peek: it is to the point, not too long,
and has some great examples on it.


Now, if you are in a rush to get started, have an account already (if not, you
will really need to start at our developer site), and want to bypass the 
documentation for now (you gotta promise to go take a look at it later),
here's a quick overview of what you can do with it:

   * For the time being, you can only use the Compete API to query Site
     Analytics data (i.e. the data you see at Compete's site profile; check 
     http://siteanalytics.compete.com/facebook.com/ for an example). 
     Search, Referrals, Categories & Keywords may (or may not) come at a later 
     date.

  * We currently only output data in JSON format. To all of you folks who 
    prefer to consume your data in XML format: if the unavailability of XML is 
    keeping you from using the API, write us at api@compete.com. If we get
    enough hate mail, our genial product manager will probably give us a
    couple of days to add xml support.

  * Check out http://apps.compete.com/sites/ to learn more about querying for 
    site data.
   
  * Check out http://apps.compete/com/sites/anysite.com/trended/ for more
    specific examples of what's available on the API today.


In case you TL;DR:

* The API returns only Site Analytics data for the time being.

* Output only in JSON

* Add a sites/ at the end of this URI for more.

* Or sites/anysite.com/trended/ for more specific info, and a few examples