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JSON Toolbox- Free online JSON tools

JSON Validator

Validate JSON online as you type. Get the exact line and column of every error, plus structure statistics for valid documents.

  • 100% client-side, nothing uploaded
  • Instant results
  • Works offline once loaded
JSON input

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How it works

About this tool

This free online JSON validator checks your JSON against RFC 8259 using the browser's native parser — the same engine used by Node.js and every modern browser. Validation happens instantly as you type, with no button to press.

When your JSON is invalid, the validator pinpoints the exact line and column of the error and shows a readable message with an excerpt of the surrounding text, so you can fix problems like trailing commas, single quotes, or missing brackets in seconds. When it is valid, you get useful structure statistics: size, line count, number of keys, nesting depth, and object/array counts.

Everything runs client-side. Your JSON never leaves your browser, which makes this validator safe for API payloads, configuration files, and documents containing secrets.

JSON Toolbox processes all data locally in the browser. Nothing is uploaded to a server.

Common questions

Frequently asked questions

How do I validate JSON online?
Paste your JSON into the editor above (or load it from a file) and it is validated as you type. If the JSON is invalid, the tool reports the exact line and column of the first error, along with an excerpt of the problematic text.
What makes JSON invalid?
Common causes are trailing commas, single quotes instead of double quotes, unquoted keys, missing commas or brackets, and control characters inside strings. JSON also does not allow comments, NaN, Infinity, or undefined values.
Which JSON specification does this validator follow?
It uses the browser’s native JSON.parse, which implements RFC 8259 (the current JSON standard, also known as ECMA-404). This is the same parser used by Node.js and every modern browser, so a document that validates here will parse anywhere.
Is my data sent anywhere when I validate it?
No. Validation happens entirely in your browser. Your JSON is never uploaded, stored, or logged, so it is safe to validate documents containing credentials, tokens, or personal data.

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