We’ve uploaded a new version of the BuiltWith Domain API – Version 12 – that lets you get additional domain attributes with your lookups.
This includes things like the amount of URLs in a sitemap of a website, the amount of custom metrics the website is reporting via Google Analytics, Tag Manager attribute loads and other number related data for websites.
Check it out via https://api.builtwith.com – as always the API is backwards compatible, you can use v1 from 5 years ago if you like!