Phisherman
IP/domain/URL reputation
Simple REST API that can scan submitted documents/files for the presence of threats.
Scanii API is a free Anti-Malware API that requires apiKey authentication, is served over HTTPS and supports CORS, so it can be called from the browser.
Scanii documentation portal
Details from docs.scanii.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.
IP/domain/URL reputation
Scan URLs in a sandboxed browser and search past scans by domain, IP, ASN, JARM or favicon hash
The Scanii API is provided by docs.scanii.com (docs.scanii.com). Scanii documentation portal
Yes. The Scanii 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 Scanii API uses apiKey authentication, so you need to register for credentials before making requests.
Yes. The Scanii API supports CORS, so front-end JavaScript can call it directly.
Yes. The Scanii API is served over HTTPS, so it's safe to use in production.