How to Tell What a Website Is Built With

Most software leaves fingerprints in what it sends over the wire, usually without any intention of doing so. A web server often names itself in its own response headers. A CMS frequently references its own file paths, like wp-content for WordPress, directly in the page it generates. A JavaScript framework often leaves distinctive markers in the compiled output it ships to the browser. None of this is secret information exactly, but very few sites go out of their way to hide it either, which is what makes technology detection from the outside possible in the first place.

• Web server: often named directly in the Server response header, such as nginx, Apache or LiteSpeed.
• CDN: frequently visible through headers a CDN adds on top of the origin server's own response, or through easily recognised hostnames its assets are served from.
• CMS: usually identified through characteristic file paths, meta tags or generator markers a given CMS leaves in its page markup.
• Framework: often visible in compiled JavaScript through distinctive global variables, data attributes or comments a build process leaves behind.
• Analytics: almost always identified directly, since analytics scripts are loaded from well known, unambiguous hostnames like googletagmanager.com.

Every result here comes from pattern matching against known signatures, which means it has the same limits any pattern matching approach has. A site can be built on a given framework while showing none of its usual markers, if it was configured unusually or if the specific version in use changed how it generates output. A confident, specific match is normally trustworthy. A result of not detected means no known signature was found, which is a meaningfully weaker claim than definitely does not use this, and should be read that way.

Run a URL through the tool to see its best guess at the web server, CDN, CMS, framework, analytics and reverse proxy in use, each reported with a confidence level rather than a flat yes or no. This is a fast way to check whether a migration to a new platform actually went live, to see what a competitor's site is built with, or to audit which third party analytics scripts a site is currently loading without digging through its source by hand.