So I\'m trying to document the format of the json returned by an api I am writing against and I\'d like to know if there is any popular format for the documentation of json stru
It may not be useful in your case since it seems you are not building an API.
But if it was the case and you were using Java or JVM (JAX-RS), you could have used Swagger.
It permits to describes your API in a JSON representation (like WSDL/WADL). And they provide an IHM layer that reads that JSON representation of your API. Here is what you will get: http://petstore.swagger.wordnik.com/
https://developers.helloreverb.com/swagger/