Why am I getting a HTTP status code of 302 when I do an API request?

Starting April 18, 2016 the API servers are redirecting any http: requests to https. If you are making an API request using http, you should change it to https to avoid this status returned.

Do I need a license to run the RxNorm/RxTerms/NDF-RT/RxClass/Interaction API?

With one exception, no license is needed to use any of the above APIs. The only exception is the getProprietaryInformation function in the RxNorm API, which requires the user to have a valid UMLS license and pass a proxy granting ticket as a parameter to the function.

Is there a limit to the number of API calls I can make?

Yes, to accomodate the increasing usage and many users of the APIs, there is a limit on the number of API calls a user can make in a given time period. Consult the Terms of Service for more details.

How will I know if I exceed the terms of service limit?

If the API call limit is exceeded, then the servers will return an HTTP status code of 403 ("Forbidden").

Do the APIs allow Cross-origin resource sharing (CORS)?