I have been seeing many people's blog that use Feedburner has that "xx readers" icon showing and wondering how many people subscribe to my blog via RSS feed and how it works.



After seeing this and some digging around, I have the answer.

Basically what it does is simple; When a feed publisher robot hit a site, it left a signiture in the HTTP USER_AGENT variable. In there, it reports how many user(s) is watching this feed. i.e.

Bloglines/3.1 (http://www.bloglines.com; 4 subscribers)

So, I enhanced NP_BotTracking to take and present the information.