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JSON Validator

Validate JSON syntax with exact line-and-column error reporting and duplicate-key detection. Client-side only — your data never leaves the browser.

Paste JSON to validate it. Invalid input reports the exact line, column, and a plain-English reason.

JSON to validate
Optional JSON Schema

What this JSON validator does

This JSON validator checks whether a document is valid JSON and reports any problem with an exact line, column, and a plain-English explanation. Paste JSON, and every error is highlighted inline in the editor. Validation runs in your browser — nothing is sent anywhere.

What counts as valid JSON

Whitespace around values is fine, but only the standard four whitespace characters. Newlines, tabs and spaces inside a value are not allowed unless escaped.
Objects must use double-quoted keys and colon-separated key-value pairs.
Strings must be double-quoted; control characters must be escaped.
Numbers must be written in standard decimal form — a leading zero like 01 is invalid.
No comments, no trailing commas, no single quotes. These are the most common JSON mistakes, and this validator flags each one at its exact location.

Frequently asked questions

How do I validate JSON?

Paste your JSON into the input pane. Validation runs automatically — valid JSON is confirmed, and invalid JSON shows the exact line and column plus a plain-English reason.

Can it detect duplicate keys?

Yes. Duplicate keys are reported as warnings so you can fix them before shipping.

Is the parser RFC 8259 compliant?

Yes. Validation follows the strict RFC 8259 JSON grammar — trailing commas, single quotes, and unquoted keys are rejected.

Does JSON Validator upload my data?

No. JSON Validator runs entirely in your browser — your input never leaves this page.

Is JSON Validator free to use?

Yes. JSON Validator is completely free, with no account and nothing to sign up for.

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Updated 2026-08-07 · Runs in your browser — your data never leaves this page.