Count RSS subscribers without Feedburner

Smashing Magazine has recently moved away from Feedburner.

Subscriber count is one of the most popular features with Feedburner. No Feedburner, no subscriber count? Not necessarily.

Facts first:

• Counting feed requests alone is quite inaccurate as many people continuously request the feed in order to have new posts the minute they get published. This BTW is in vain because Smash’s feed gets updated every 30 minutes no matter what.
• Users cannot be distinguished by IP address alone either as there are proxy servers or NAT environments. Users in such environments share a single IP address.
• Feed aggregators often use several IP adresses. Also their user agent strings change from time to time.

My approach was to hash user agent data such as User Agent string, browser language altogether with the remote ip address. This information gets hashed to “7815696ecbf1c96e6894b779456d330e” for example. If there are two users behind a proxy server they share the same IP address. While not impossible, there is a good chance they do not use the same program with the same settings. Hashing these information leads to fairly unique IDs.

How does the Feed script handle feed aggregators? Basically it scans for services’ names such as Netvibes, Bloglines and so on and aggregates requests. Fortunately many of those services give the amount of readers they aggregate in their user agent string and a unique aggregation ID. The server script parses this information and adds them to the stats. Though not all of the aggregators do it this way so there is a large margin of error.

Conclusion: Counting RSS subscribers is not exactly rocket since. Smash’s own subscriber count does correlate pretty well to Feedburners count. This approach seems to do the job. If you are still using Smash’s old RSS address, please update now.