JSONLint

JSONLint ist ein Validator (Syntax-Überprüfer) und Formatsetzer (setzt neue zeilen, Abstände etc.) für JSON, ein einfaches Daten-Austauschformat.

Sure, a few. You can input a URL and it'll scrape it for JSON and parse that.
An example URL to test: http://www.reddit.com/r/programming/comments/9szpc/jsonlint_a_handy_json_validator_and_reformatter.json

You can also provide JSON to lint in the URL if you link to JSON Lint with the "json" parameter. Here's an example URL to test.

Additionally, JSON Lint can also be used as a json compressor if you add ?reformat=compress to the URL.

Expecting 'STRING'

You probably have an extra comma at the end of your collection. Something like: { "a": "b", }

Expecting 'STRING', 'NUMBER', 'NULL', 'TRUE', 'FALSE', '{', '['

You probably have an extra comma at the end of your list. Something like: [ "a", "b", ]
You also may have not enclosed your collection keys in quotes. Proper format for a collection is: { "key": "value" }

Be sure to follow JSON's syntax properly. For example, always use double quotes, always quotify your keys, and remove all callback functions.

If you and your friend are on different systems (Win/Unix), this is possible due to the way windows handles newlines. Essentially, if you have just newline characters (\n) in your JSON and paste it into JSONLint from a windows machine, it can validate it as valid erroneously since Windows may need a carriage return (\r) as well to detect newlines properly.

The solution: Either use direct URL input, or make sure your content's newlines match the architecture your system expects!

Chris Dary built this for the Arc90 Lab. Much is owed to the community (this uses Zach Conner's javascript Pure JS JSON parser, for example).