Symbolic and Arithmetic Math Calculator.
Newton API is a free Science & Math API that requires no API key, is served over HTTPS and does not support CORS, so it should be called from a server.
Details from newton.vercel.app.

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 Newton API is provided by newton (newton.vercel.app).
Yes. The Newton API is listed in the Science & Math 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 Newton API requires no authentication, so you can start making requests without signing up.
Not directly. The Newton API does not allow CORS, so call it from a server, serverless function or proxy instead of front-end JavaScript.
Yes. The Newton API is served over HTTPS, so it's safe to use in production.