Really clean design. I generated a bunch of complex deeply strucutred dummy JSON data and the resulting visual wasn't bad!

I like the name too! A small suggestion is don't force yourself to call it Jsontr.ee because of the cool domain. Getting to the line "Render the Tree Diagram: Use the jsontr.ee function to visualize the JSON data." -- Just use jsontree :-)

+1 for the JSONTree naming.