BuiltWith is a “website profiler, lead generation, competitive analysis and business intelligence tool providing technology adoption and usage analytics for the internet.”
BuiltWith is a very useful tool for finding out what services and technologies are being used on any given website. The tool has a Firefox and Chrome extension available which makes it a lot more accessible for the geeky type.
As you will see in the example below where I run the add-on on this blog, the tool spits out all sorts of useful information such as the server and frameworks being used (Apache and PHP), the software platform (WordPress), any advertising being used (AdSense), tracking technologies such as Google Analytics, any content delivery networks and much, much more.
Almost every, if not all, technologies have a uniquely identifiable structure, syntax, response or what ever you want to call it. if you know what you are looking for then you know the technology being used.
For example, Drupal CMS versions over 4.6 have a unique expires header of ‘Sun, 19 Nov 1978 05:00:00 GMT‘. Of co
I suspect this type of fingerprinting is what BuiltWith uses in order to scrape all of this information out.
Of course you should not take such tools to be absolute truth as there are ways to evade basic fingerprinting but generally speaking, they will be quite accurate.