SEOmoz which recently changed to new brand name Moz is one of the biggest SEO Analytics provider. This company provides API for developer in many packages, we are using its free API package to give you results for any URL. Also we are using same API program from Mozscape to power our best SEO Tool which we provide to use for free.
Moz Checker Tool will return Page Authority, Domain Authority, MozRank, Backlinks, HTTP Status, Subdomain MozRank, External Follow link number as result for any URL.