Every developer has wondered at some point: what is this site built with? Maybe you’re doing competitive research, reverse-engineering a stack decision, or just curious how a particularly fast site achieves its performance. Tools like Wappalyzer answer this question instantly. But how do they actually know? The answer is more interesting than you’d expect and involves four distinct layers of analysis working simultaneously. Layer 1: HTML Source Analysis The most obvious place to start is the raw HTML. Websites leave fingerprints everywhere in their markup, and most of them aren’t trying to hide. Generator meta tags are the easiest signal. WordPress sites often include: Webflow embeds its own attributes throughout the DOM: CSS class patterns reveal frameworks. A site with hundreds of classes prefixed with wp- is almost certainly WordPress. Classes like w-nav, w-container, or wf- point to Webflow.…