The JSON options are not documented in the user manual yet (I should add it soon). Here is the list of available commands:
http://x.x.x.x/jo: returns options.
http://x.x.x.x/jc: returns controller variables.
http://x.x.x.x/jp: returns program data.
http://x.x.x.x/jn: returns station names and data.
http://x.x.x.x/js: returns station status bits.
from the variable name you should be able to figure out the meaning of each variable.