Render Json files

I created www folder and contained here my_file.json with text {{ app_name }}.
After that I created And wrote here the code:

context.app_name = 'my_app'
return context

But jinja does not work when I tried to trigger this function

UPD: IT works only when you use html extension. How to use with json?
UPD2 : Also it is works with xml extension
UPD3: I understood, that in Enviroment class( exists function add_extension
UPD4: Inside exists function def is_static_file.