I am using jquery, JSON, and AJAX for a comment system. I am curious, is there a size limit on what you can send through/store with JSON? Like if a user types a large amount and I send it through JSON is there some sort of maximum limit? 

Also can any kind of text be sent through JSON. for example sometime I allow users to use html, will this be ok?
['https://Stackoverflow.com/questions/1262376', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/143030/']
JSON is similar to other data formats like XML - if you need to transmit more data, you just send more data. There's no inherent size limitation to the JSON request. Any limitation would be set by the server parsing the request. (For instance, ASP.NET has the "MaxJsonLength" property of the serializer.)
It depends on the implementation of your JSON writer/parser. Microsoft's DataContractJsonSerializer seems to have a hard limit around 8kb (8192 I think), and it will error out for larger strings.

Edit:
We were able to resolve the 8K limit for JSON strings by setting the MaxJsonLength property in the web config as described in this answer: <https://stackoverflow.com/a/1151993/61569>