BuiltWith

How did Gary build the initial version of BuiltWith?

Gary started building scrapers and a database of technologies by mapping specific pieces of code to identify the technology stack used by various websites. Immediately after the official launch, he noticed an increase in traffic.

article

builtwith.com : internet archive

BuiltWith offers a free version that shows the technology stack used by your competitors, while the paid version provides access to a vast database of everything available on the internet.