I’ve been using Google PageSpeed Insights quite a bit recently. There isn’t much information on how exactly the tests are run, which can make it hard to reproduce the results. Then I noticed the user agent strings coming from PageSpeed Insights ( emphasis mine ):
Desktop
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko; Google Page Speed Insights) Chrome/27.0.1453 Safari/537.36
Mobile
Mozilla/5.0 (iPhone; CPU iPhone OS 6_0_1 like Mac OS X) AppleWebKit/537.36 (KHTML, like Gecko; Google Page Speed Insights) Version/6.0 Mobile/10A525 Safari/8536.25
The only difference between these and normal user agent strings is the ; Google Page Speed Insights
.
If these user agent strings are what they claim to be, the Insight desktop is using Chrome 27 released in May 2013 and Insight mobile is using Safari from iOS 6 released in Nov 2012.
This explains some of the inconsistency I noticed in comparing PageSpeed Insights results with Chrome mobile device emulation.