As noted in the comments by @brad, @ jessie-a-morris, @tknew, there is no easy-to-use method that can be easily repeated in your own analyzer.
Quote from w3techs own information:
http://w3techs.com/faq especially the chapter "How does your website analyzer work?" explains
... We look for specific patterns on web pages that identify the use of technology, just like a virus scanner looks for patterns in a file to identify viruses. We use a combination of regular expressions and a DOM traversal for this search. We have identified several thousand indicators for the use of technology. These indicators have different priorities and are based on the presence or absence of specific combinations of indicators in a specific context, we come to our conclusions.
These are examples of information used by indicators:
- Webpage HTML Elements
- Specific HTML tags, such as a generator meta tag
- JavaScript code
- CSS code
- Site URL structure
- External links
- HTTP headers like cookies
- HTTP responses to specific requests, such as compression
It took a lot of research to create the analyzer, and we are constantly improving it. We want this to be the best web site analyzer ...
and http://w3techs.com/disclaimer indicates that
... To receive any information from websites, we rely on the websites themselves, their owners or their webmasters to provide such information. Some websites are more open to sharing this type of information than others. Some technologies may provide more opportunities for disclosing information about their use than others ...
and more “we cannot”, “in some cases”, “some technologies”, “inaccurate results” should