Here is an API v3 endpoint for roles for the Feature Developer role in HolacracyOne's GlassFrog circle:

https://api.glassfrog.com/api/v3/roles/1787

When you make an HTTP GET request to this endpoint (with a valid API key) you will receive a JSON object in return that details the role with ID 1787.

 

This object includes a "roles" section and a "linked" section.  Note that the "roles" section includes multiple ids for accountabilities, people, domains and circles with no extra data.  This data is included in the "linked" section of the JSON object.  By matching the IDs from the different sections, you can piece together the full role description.