API for getting Pincode details in India.
PostalPinCode API is a free Tracking API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Api - Postal PIN Code
Details from postalpincode.in.

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An API to query Brazilian ZIP codes and orders easily, quickly and free
The PostalPinCode API is provided by Api for Indian Postal PIN Code (postalpincode.in). Api - Postal PIN Code
Yes. The PostalPinCode API is listed in the Tracking 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 PostalPinCode API requires no authentication, so you can start making requests without signing up.
CORS support for the PostalPinCode API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The PostalPinCode API is served over HTTPS, so it's safe to use in production.