2 services carry this tag in their source record. Tags come from the provider, not from us — a tag is a claim about what the service does, not proof that it does it well.
Does a website use polyfill.io? Fetches the page (homepage for a bare domain) and matches polyfill.io's fingerprints in the HTML and response headers, returning yes/no with the evidence snippet and the category (library)...
Change watch for does site use polyfill: runs the check, compares it with the result from your previous call for the same domain (kept 90 days) and returns the current answer, changed true/false, the fields that changed...