Otto provides API endpoints to perform tasks (e.g., migration, file download). The intent is to encourage developers to interact with the Otto in any way that they see fit.
Since the inclusion of cURL and JSON support in FileMaker version 16, the Otto API is available from FileMaker Scripts. Now you can use your FileMaker skills to create custom migration solutions and other server automation tasks. You can also use any HTTP client (e.g., Postman) to interact with Otto.
The Migrator file that ships with Otto is just one example of how to perform migrations. You can use it as is, or borrow any code in your own customer solutions.
The API is exposed via a RESTFul JSON API. Authentication is either with Basic Auth or AccessToken.