Track Estimated Cost for Your AppEngine Site With Firefox Add-on

If you were careful reading Google App Engine documentation, you could have read this: “If you access your site while signed in using an administrator account, App Engine includes per-request statistics in the response headers. The header X-AppEngine-Estimated-CPM-US-Dollars represents an estimate of what 1,000 requests similar to this request would cost in US dollars.”

Well, although I’ve been using GAE periodically for the last several months, I became aware of the above just last week. I guess during the first several weeks a developer need to adapt and put his way of thinking in line with App Engine. However, when the things settle and one is more comfortable with the environment, a different kind of questions start to pop up… How can you put a price tag on your SaaS offering without knowing how much would it cost you in the first place? How do you know where to draw a line with your “free use plan” and which conversion rate do you need for a sustainable growth?

Obviously, the estimated cost information is simply too useful to be ignored. Unfortunately, I could not find a ready to use solution so I used my modest knowledge of programming a Firefox extension and made an add-on that for an App Engine site shows the total estimated cost in the Firefox status bar:

Feel free to download GAE Cost add-on for Firefox and use it with your GAE applications. Please notice that:

  • you have to be signed in using an administrator account (via Google), and

  • stated cost are for 1000 similar requests.

You can reset the cost counters using options in the context menu of the label.

To find out a cost of a particular request, open Firefox Error Console. There you can find not only cost information but also resource usage details (server-side time, app server CPU time, and API CPU time) for each request.

If you find some requests more “expensive” than expected, you can use an excellent Appstats profiling tool available with the latest GAE SDK to find out what’s going on.

Hope you’ll find this useful.

Update 2011-04-07: Add-on was updated for Firefox 4.0.