I don't know what you are asking. There are certainly editors which
help you write valid json, but it isn't complicated. Prototype should
accept any valid JSON that you write. Typically what you want to do
is to build a structure or array of data in your server scripting
language, then use an appropriate library to "serialize" the structure
or array into JSON which you return to the browser.
For how to write proper JSON as well as a list of various JSON
libraries in multiple languages, go to
json.org