JSON URL formating

JSON URL formating

What type of parameters can I have on the JSON URL? I want to filter something like category != "". I want an not-equal. So it would be like:

https://www.mysite.com/category.json?cate!=""

Or:
https://www.mysite.com/category.json?cate!=empty

Or:

https://www.mysite.com/category.json?cate!=null