Blog Tool, Publishing Platform, and CMS — WordPress
We detected the following sites were using Wordpress
A CMS will sometimes include a meta tag within the html of each page. This is usually a "generator" tag like <meta name="generator" content="What CMS" /> but could also be "application-name", "Powered-By" or anyting else the CMS creators decide to use.
If a CMS doesn't have meta tags, it will often have other uniquely identifiable html markup. This can range from unique html comments, ids or classes.
Some content management systems also offer hosting. A website hosted on a CMS developer's domain is a dead giveaway.
HTTP headers, including cookies, can be used in same situations to identify a CMS.