Network calculators, including subnets, DNS, binary, and security tools.
NetworkCalc API is a free Development API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
The NetworkCalc REST APIs allow you to programmatically access the functionality of our network tools. We offer simple HTTPS interfaces with JSON responses.
Details from networkcalc.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.
The NetworkCalc API is provided by NetworkCalc (networkcalc.com). The NetworkCalc REST APIs allow you to programmatically access the functionality of our network tools. We offer simple HTTPS interfaces with JSON responses.
Yes. The NetworkCalc 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.
No. The NetworkCalc API requires no authentication, so you can start making requests without signing up.
Yes. The NetworkCalc API supports CORS, so front-end JavaScript can call it directly.
Yes. The NetworkCalc API is served over HTTPS, so it's safe to use in production.