This API was created by Salesforce. The Salesforce.com Metadata API endpoint is located at http://soap.sforce.com/. You can find the Salesforce portal / hompage here. The Salesforce.com Metadata API is not currently available on the RapidAPI marketplace.
Click "Request this API on RapidAPI" to let us know if you would like to access to this API.
Meanwhile, you can check out the top APIs that currently available for developers.