How to know if a server is running Node.js?

Question

I was wondering how w3techs knows when a given server uses Node.js. http://w3techs.com/technologies/details/ws-nodejs/all/all

I'm guessing they look at some specific http headers.

For example: X-Powered-By:Express

But not every node module generate such headers.

Do you know any other ways or similar fingerprints generated by popular node modules ?

Answer 1

As already pointed out by comments by @brad, @jessie-a-morris, @tknew there is no easy to use method available that you might easily reuse in your own analyzer.

Quoting from w3techs's own information:

http://w3techs.com/faq especially chapter "How exactly does your website analyzer work?" explains

...We search for specific patterns in the web pages that identify the usage of technologies, similarly to the way a virus scanner searches for patterns in a file to identify viruses. We use a combination of regular expressions and DOM traversal for this search. We have identified several thousand indicators for technology usage. These indicators have different priorities, and based on the presence or absence of specific combinations of indicators in a specific context, we come to our conclusions.

These are examples of the information used by the indicators:

• HTML elements of web pages
• Specific HTML tags, for example the generator meta tag
• JavaScript code
• CSS code
• The URL structure of a site
• Offsite links
• HTTP headers, for example cookies
• HTTP responses to specific requests, for example compression

A lot of research was necessary to build the analyzer, and we keep improving it all the time. We want it to be the best possible website analyzer...

and http://w3techs.com/disclaimer points out that

...In order to obtain 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 means to reveal information about their usage than others...

and more "we may not", "in some cases", "some technologies", "inaccurate results" follows