How do you determine what technology a website is built on?

You could use http://builtwith.com to figure out which server and programming language was used. For example it told me that SO uses IIS7, google analytics, html4 and utf8.

If you want to know the framework...well that will probably not be possible just from looking at the site. Why don't you write them an email? ;)

There are all sorts of things you can look out for, but it doesn't really give you any certainty as to the technology behind a site. In general, information like that is something people will want to hide, as the more information that is exposed the easier it might be for malicious parties to identify security vulnerabilities or denial of service holes.

If I was interested I'd probably look, in no particular order, at:

• urls, and file extensions.
• HTTP response headers
• Source code for comments, or standard JS libraries

Incidentally, the tools mentioned in other answers are only looking at some of the above properties of the site for you, albeit automatically, and slightly quicker. :)

I use 1 plug in for Firefox that gives me the IP and country for the hosting website and it's Web Server name called Domain Details, and for javascript framework I use WTFramework

I still need to wonder what script it was written on, but it is a start :)

Hope it helps.

P.S. the output will be something like this:

alt text http://img88.imageshack.us/img88/2505/200812282328ha0.png

URLs can give a lot of clues, especially with Content Management Systems.

For example "http://abcxyz.com/node/46" looks a lot like Drupal.

Also many frameworks have standard JavaScript and CSS files they use.

Some people might even deliberately obscure the technology they use. After all, it wouldn't take me long to tweak apache so that ".asp" actually ran perl scripts and put "powered by Microsoft IIS" into my footer despite the fact I used MySQL.

That way you'd spend all your time trying to hack my site using vulnerabilities it doesn't actually have.

Examining the cookies the site gives can reveal the underlying framework. CodeIgniter, for example defaults to a telltale ci_sessions cookie. Sites using PEAR Auth will do something similar.

Most ASP.NET sites are easy to identify from the .aspx in the URLs. There are also telltale signs in the HTML source, like a hidden form field named __VIEWSTATE or the WebResource.axd JavaScript. HTML elements will often have id attributes starting with something like _ctl0.

Rails sites will usually include stylesheets from /stylesheets and JavaScript files from /javascripts and each URL will usually have a query string containing a timestamp to thwart caching. Form fields will often follow the naming convention of model_name[attribute_name].

You can use domaintools.com to lookup the server information for a website and narrow down to whether it's open source / Microsoft:

http://whois.domaintools.com/stackoverflow.com

And after that it's a matter of looking in the footer for tip-offs such as "Powered by WordPress" or "vBulletin" etc.

yes there are some telltale signs for common CMSs like Drupal, Joomla, Pligg, and RoR etc .. .. ASP.NET stuff is easy to spot too .. but as the framework becomes more obscure it gets harder to deduce ..

What I usually is compare the site i am snooping with another site that I know is built using a particular tech. That sometimes works ..

Go to Netcraft and use the "What's that site running?" search box in the top left corner. Click here for the report on Stack Overflow. It won't necessarily be correct (e.g., there could be caching or load balancing in the way), but it often gives you the clue you need.

There is also W3Techs, which shows you much of that information.

http://www.quarkbase.com/ is a very nice tool and information website