
Google Link/Domain Flagging.
Google Safe Browsing API is a free Anti-Malware API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
APIs to access the Google Safe Browsing lists of unsafe web resources.
Details from developers.google.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.
Provide malware datasets and threat intelligence feeds
IP/domain/URL reputation
Malware Archive / file sourcing
The Google Safe Browsing API is provided by Google Safe Browsing (developers.google.com). APIs to access the Google Safe Browsing lists of unsafe web resources.
Yes. The Google Safe Browsing API is listed in the Anti-Malware 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 Google Safe Browsing API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Google Safe Browsing API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Google Safe Browsing API is served over HTTPS, so it's safe to use in production.