How do we check what programming language a website is using?
I mean something like this:
www.domain.com
How to check its using html, php, aspx, ruby on rails or etc?
I only want to know the mainpage (www.domain.com), not the sub-page (www.domain.com/about/).
From a theoretical point of view, it's impossible, because you can just have the webserver serve up whatever extension you like, and hide appropriate headers.
In practice, it's easy.
Just append "index.php" or "index.aspx" or similar, until you find one that works :) But as above, if they want to hide it, this doesn't confirm anything.
Point of order: They all use HTML.
In other news; various frameworks and langauges send X-Powered-By HTTP headers, some sites are truthful in their use of file extensions, and some sites actively work towards hiding the programming language in use. And even if index.php works, that doesn't mean they are using PHP; it could mean that they have their server set up to pretend .php means ASP.NET; just as easily.
The best way of telling is usually to look at the produced HTML; most languages carry with them styles of HTML; some more telling than others. (ASP(.NET) sites are usually frightfully easy to spot.)
A better question, perhaps, is Why do you care? What does it matter to you what language the site is written in?
You can't possibly tell.
e.g. if you look At Amazon's home page, that will talk to approx 100 different services to populate various sections of the page. You can't determine what language those services are written in (I believe Amazon uses a variety of different languages).
It should theoretically be impossible to tell, but you can scan the HTTP header and html for artifacts, as well as the file extensions used in URLs.
Netcraft uses several advanced methods to determine the operating system a host is running, which is at least marginally related to determining what kind of software a host is running.
I sometimes type in /admin in the url to see if the site is built with Django. Those who do rarely changes the default login template.