Test and Check or Verify GZip Page Compression on Your Website
When a web page is sent in response to request from web browsers, its header will include a line to indicate the type of the web page the web server is sending over. Typically, the header will have a line of “Content-Encoding: gzip” if the web page is compressed.
Thus, by viewing the header of the web page, user can determine if the web page is compressed or not. Unfortunately, the header of HTTP response is well hidden, but several web developer box, which are the add-ons or add-ins for web browsers, can allow user to view the header information