I keep a boilerplate Rails 5 API-only app among my repos for rapid API building, but sometimes I just want a basic structure to query against (without having to deal with a complete stand alone Rails app).

Enter: json-schema-faker and json-server

Cory House has put together a great tutorial on how to build and serve a json database in 3 easy steps:  https://medium.freecodecamp.org/rapid-development-via-mock-apis-e559087be066