Private JSON syntax checker

JSON Validator Online

Paste or open JSON to check its syntax and see each detected error or warning with a useful explanation and location.

Your JSON stays in your browser. It is never uploaded.

Private by design. Validation happens in this browser. Your source is not uploaded.

    What the JSON validator checks

    The validator accepts every JSON root type, including objects, arrays, strings, numbers, booleans, and null. It reports syntax that prevents parsing and warns when the same property name appears more than once in one object.

    Duplicate names are an interoperability problem: different software may keep the first value, the last value, every value, or reject the document.

    Frequently Asked Questions

    It checks whether the source follows JSON grammar and warns about duplicate property names that can behave differently between programs.

    JSON is stricter than JavaScript object syntax. It requires double-quoted property names and strings and does not support comments, functions, undefined, or trailing commas.

    RFC 8259 says names within an object should be unique. Parsers often accept duplicates but may disagree about the result, so this validator treats them as warnings.

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