> Today, PHP is used by more than 80% of all the websites _whose server-side programming language we know_

I find it pretty annoying that they don't post stats on the websites that they couldn't classify. I think it's likely that their survey suffers from some level of survivorship bias: only websites that loudly announce their tech stack get counted.

So, how do they know which programming language is being used by a server? From https://w3techs.com/faq, they look at:

- HTML elements of web pages

- Specific HTML tags, for example the generator meta tag

- The URL structure of a site

- HTTP headers, for example cookies

- HTTP responses to specific requests, for example compression

I typically run Python / Django sites, and the only way, that you would know I'm running Python is a few Django-specific security/auth cookies. _Maybe_ that stuff gets picked up by their crawler. If I was running another Python web framework, like Flask, then you'd have no idea what kind of app server was sitting behind NGINX.

I suspect an enormous number of those are WordPress blogs and MediaWiki sites, and I don't feel like that number is very useful without breaking those out. It's a bit like saying Fortran is popular in data science because SciPy is implemented partly in Fortran — not so much an indicator of overall language health as it is an artifact of one product's popularity.