• UML Modeling tools are very complex
• UML Diagrams appear very technical
• UML Diagrams are not taken seriously
• UML Diagrams are ugly

JSON Designer is easy to use and the models look nice.

• Requirements management is crucial for project success
• Requirements management is greatly supported by diagrams
• Requirements management is about efficiently depicting complexity
• Requirements management is the contract of what people expect 
• Requirements management is the contract of what people create
• The core of APIs is the contract between the server and client code
• There is currently no specific diagram type for hierarchical structures
• JSON structures are still depicted by example code not by diagram in API documentations, see Google, Facebook and the likes

You should do requirements modeling!
JSON Designer is specially targeted for today's API management.
It's free.