Note: This is currently a personal proof-of-concept project, and is not affiliated with any of the organizations listed above. (Though they are all awesome, and totally worth checking out.) This ...
JSON Editor takes a JSON Schema and uses it to generate an HTML form. It has full support for JSON Schema version 3 and 4 and can integrate with several popular CSS frameworks (bootstrap, foundation, ...
Once you've created a JSON Schema that describes a JSON document, you can use it both in Visual Studio -- to provide guidance when creating JSON documents -- and in your code to validate the messages ...