API is intended to explore and visualize trends/patterns across the US innovation landscape.
PatentsView API is a free Patent API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
The Open Data Portal (ODP) is USPTO's data platform that empowers you to discover and easily extract USPTO data in one place for free.
Details from patentsview.org.

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Yes. The PatentsView API is listed in the Patent 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 PatentsView API requires no authentication, so you can start making requests without signing up.
CORS support for the PatentsView API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The PatentsView API is served over HTTPS, so it's safe to use in production.