Phone number validation.
Numverify API is a free Phone API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Numverify API is a powerful JSON API providing international and national phone number validation, carrier, location, and line type lookup for developers.
Details from numverify.com.

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The Numverify API is provided by Numverify API (numverify.com). Numverify API is a powerful JSON API providing international and national phone number validation, carrier, location, and line type lookup for developers.
Yes. The Numverify API is listed in the Phone 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 Numverify API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Numverify API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Numverify API is served over HTTPS, so it's safe to use in production.