We have received a bunch of requests of late regarding our online tools to test your Web sites and applications for the impact of Port80 Software tools, especially for HTTP compression:
http://www.port80software.com/support/p80tools
In general, online compression testers may or may not capture the truth about compression, depending on how well they were written to emulate browser functionality. For instance, some online tools cannot handle chunked encoded data properly, and there are number of other such limitations that are quite common. Programming for browser emulation is still, shall we say, a work in progress (as are most browsers themselves).
In fact, our own "Compress Check" is intended primarily as an online sales tool and has often failed to show compression when we know independently that it is taking place (send us a bad link to a report, and we will work to get it fixed). Our Python code is good, but it ain’t perfect for online HTTP analysis. Also, intermittent network transience can also get in the way of any 100% perfect HTTP analysis session…
This is why, as a rule, Port80 recommends that you examine the HTTP traffic directly -- with independent, third party tools -- in order to verify compression or the impact of any IIS or HTTP technology. We document how to do this in our httpZip evaluation guide, the second section of which contains links to the kind of tools you will need in order to do an independent evaluation of any compression solution. This will also point you to a good 200 OK blog post with benefits of various third party HTTP analysis tools:
http://www.port80software.com/200ok/archive/2005/06/15/606.aspx
If you have a Port80 Software product installed on IIS and think everything should be kosher – but our online tools like Compress Check are saying otherwise – please contact us so we can help. Free support is a good thing.
Best regards,
Port80