JSON Validator for Notepad++? [closed]
You might be able to use a JSON formatter to accomplish the task (since it would likely complain or do something wrong -- say, like indent improperly -- if the JSON's invalid). See Is there an extension to reindent JSON in Notepad++?. Similarly, there's a JSONViewer Notepad++ plugin the might help in the same way.
Another less-than-ideal alternative would be to just use one of the online JSON validators.
There is plugin for NPP+ called JSLint. It is a plugin to validate JavaScript-code, but it works also just fine with JSON-files.