Sorry to reply so late, but I thought it's worth mentioning that AppGameKit does have some built-in JSON commands. For example, Types can be converted to and from JSON like so:
type spritetype
ID as integer
x as float
y as float
width as float
height as float
endtype
MyType as spritetype
MyType.fromJSON( '{"ID": 4, "x": 10.5, "y": 20, "width": 50.1, "height": 20.45}' )
var1 as string
var1 = MyType.toJSON()
(Taken straight from the docs)
Arrays can also be saved and loaded as JSON really easily using MyArray.save("filename.json") and MyArray.load("filename.json").
Can be tricky to find info on this in the docs as it only appears under Guides/Arrays Enhanced, so they don't offer much help when pressing F1, but these built-in JSON commands are super useful and work great.