How to walk a C# object hierarchy and create JSON string?

I am creating a metadata site for our API. It is like swagger implementation. Currently I am facing difficulty with creating a sample JSON representation of our request response objects. These are complex objects that may even contain lists.

Right now I am at the point where via using reflection I am able to find all the request and their corresponding response objects.

Is there a library that can convert a reflection

assembly.GetType("FullyQuallifiedObjectName")

output to a JSON sample string? My research so far has not been fruitful.