API for calculating and comparing metrics of different websites using Page Rank algorithm.
Open Page Rank API is a free Development API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Get a 0-10 authority score and full monthly history for any domain, up to 100 in one API call. Start free with 30,000 domains a month.
Details from domcop.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Yes. The Open Page Rank API is listed in the Development category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Open Page Rank API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Open Page Rank API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Open Page Rank API is served over HTTPS, so it's safe to use in production.