Check whether JSON is valid and get the precise line and column of any error, plus structural statistics.
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Validation answers one question — does this parse — and points at the exact line and column where it stops if it does not. Most real JSON errors are dull and easy to miss by eye: a trailing comma, a single quote where a double belongs, an unescaped newline inside a string, or a stray byte-order mark at the start of a file.
Note what this cannot tell you. A document can parse perfectly and still be wrong for its purpose, with a number sent as a string or a required field absent. That is a schema question, and the JSON Schema Validator is the tool for it.