Each OpenFisca Country Package web API comes with a set of endpoints including an OpenAPI specification on the /spec route.
You can check out the demonstration swagger documentation to see how the endpoints work.
The Openfisca Web API can be used to:
/parameters), the variables (e.g. /variables), and entities (e.g. /entities) of the Country Package,/calculate) on a specific situation. To describe a situation, learn more about the Web API inputs and outputs.