May I ask why would you insist on such a thing? Is it about avoiding SQL?

I'd like access to JSON Schema's impressive tooling. I haven't seen anything like this for SQL schemas: http://jeremydorn.com/json-editor/

(Though if it exists please tell me, I'd be very interested!)

Don't know for Web-Applications, but for Windows Applications there are tons of framework, which will create GUIs for you, given your Model.

One very good, which I extensively used in my previous position was DevExpress (https://www.devexpress.com/Products/NET/Controls/WPF/Editors...).