Jsonlint provides the missing json validator… simply but usefull
Ever needed to know if your string is a valid json encoded string ? Well, jsonlint gives you the ability to quickly check and see if your string is a valid json string. Even better, your json string will be indented in order to have a better visibility. Note, you can also paste an url whitch will be parsed by this cool and simple json validator.
JSONLint - http://www.jsonlint.com/