: How to reliably determine server stack of a site (eg .Net vs Open Source) I've been trying to figure out how to determine the use of the .Net stack compared to Open Source OS's. I have read

@Jennifer507

Builtwith seems to be pretty good for this.

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@LarsenBagley505

This is a pretty good overview of the StackExchange network and their technologies meta.stackexchange.com/questions/10369/which-tools-and-technologies-build-the-stack-exchange-network
There are probably more reliable ways to determine the operating system of a server such as using nmap and try and see what ports are open on a server. It's not a 100% guarantee but probably more than what Netcraft uses.

Netcraft also goes over their accuracy and specifically OS detection uptime.netcraft.com/accuracy.html#os

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@Yeniel560

Surveys like Netcraft just take a sample of what they can find and what servers make available to them.

There's no way to be 100% certain of what stacks are really used, for the following reasons:


Any server can alter the Server header it sends (and any header in fact).
URL-rewriting could can hide the mechanism used to render the page, e.g. .asp or .php. You're never actually sure that a .html really is a static file (and twisted webmasters could very well choose to call their PHP scripts .asp and make them run by mod_php on an Apache Httpd server).
Some more complex configurations could involve reverse proxy servers for part of a site, whereby the actual handling of the request may be done by different stacks.
Reverse proxy servers (load balancers) can hide the real server technology used.

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