TestMace allows not only to create API description manually, but also to import an existing documentation from Swagger 2.0 and OpenAPI 3.0.
You can import API description right from the + context menu by choosing Import -> Swagger (there is the same menu in the Scratches area as well):
You'll see the next dialog:
As you can see, both import from file and downloading API from the remote server at a specific URL are supported. The imported description is added to the project tree after you click on the OK button.
You can also update an existing API description. To do that, choose Update api from the ApiRootFolder context menu. You'll see a dialog similar to the import API dialog. All changes you make in API description will be canceled after the update.