JSON Validator
Validate JSON syntax and get detailed line-by-line error messages.
What is JSON Validation?
JSON validation checks whether a string conforms to the JSON specification (RFC 8259). Valid JSON must use double-quoted strings, have no trailing commas, and contain properly nested braces and brackets. Unlike YAML or TOML, JSON has a strict syntax with no room for ambiguity.
Validating JSON before parsing it prevents runtime errors in applications. A single misplaced comma or unescaped character can cause a parse failure that breaks an entire data pipeline.
Common JSON Syntax Errors
The most frequent JSON mistakes are trailing commas (e.g., {"a": 1,}) which are valid in JavaScript but not JSON. Using single quotes instead of double quotes is another common error — all JSON strings must use double quotes.
Other issues include missing commas between array elements, unescaped backslashes or control characters inside strings, and using JavaScript-specific values like undefined or NaN which are not valid JSON types.
JSON vs JavaScript Object Notation
Although JSON stands for JavaScript Object Notation, it is stricter than JavaScript object syntax. In JavaScript you can use unquoted keys, single quotes, and trailing commas. JSON requires double-quoted keys, double-quoted strings, and no trailing commas.
This distinction matters when copying data from JavaScript source code into a JSON file or API request body. Always validate after copying to catch these subtle differences.
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Frequently Asked Questions
What makes JSON invalid?
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Common JSON errors include: trailing commas after the last element in arrays or objects, single quotes instead of double quotes for strings, missing quotes around object keys, unescaped special characters in strings, and mismatched brackets or braces.
Does this validator show the exact error location?
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Yes. When JSON is invalid, the validator reports the character position and attempts to identify the line and column number where the error occurred.
Is my data kept private?
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All validation runs entirely in your browser. No data is ever sent to any server.
Can I validate large JSON files?
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Yes. This tool processes JSON using your browser's native JSON.parse, which can handle files up to hundreds of megabytes depending on your device's memory.