See JSON in TiddlyWiki for an overview of using JSON in TiddlyWiki.

Text References for Accessing JSON Data

Text references are a simple shortcut syntax to look up the value of a named property. For example, if a DictionaryTiddler called MonthDays contains:

oct:31
nov:30
dec:31

... then {{MonthDays##nov}} will resolve to the value 30.

The same is true if MonthDays is a JSONTiddler with the following content:

{"oct":31,"nov":30,"dec":31}