JSON Validator — Check & Fix JSON Syntax Online

JSON input

✓ Valid JSON ✗ Invalid

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How to use JSON Validator

Paste your JSON — from an API response, config file or export.
Read the verdict instantly — valid, or the exact error with its location.
Fix the flagged character — trailing comma, single quote, unquoted key are the usual finds.
Re-validate until clean, then format or minify with the companion JSON tools.

What is JSON Validator?

A JSON validator checks whether text is syntactically legal JSON — and when it isn't, points at the exact character where parsing fails. JSON's grammar is strict on purpose: double quotes only, no trailing commas, keys always quoted, no comments — and a single violation makes the entire document unparseable.

The usual suspects are exactly those strictnesses: a trailing comma after the last array item (legal in JavaScript, fatal in JSON), single quotes from a Python paste, an unquoted key, a raw line break inside a string, or smart quotes introduced by a word processor. Each produces a cryptic parser error downstream; a validator names it here first.

About the JSON Validator

Paste your JSON and get an instant verdict: valid, or invalid with the error and its position — so you fix the actual character instead of bisecting a config file by trial and error.

When it saves the day: an API returns "unexpected token" and you need to know if the payload or your code is at fault; a config file (package.json, composer.json, app settings) breaks an app after a hand-edit; data exported from one system won't import into another; or a colleague's "JSON" turns out to be a JavaScript object literal with comments and single quotes. Validation runs entirely in your browser — API keys and private payloads never leave your machine.

Once valid, the neighbors take over: JSON Formatter pretty-prints it, JSON Viewer explores it as a tree, and JSON Minifier compacts it for shipping.

Frequently Asked Questions

Trailing commas ({"a":1,}), single quotes instead of double, unquoted keys ({key: 1}), comments (JSON has none), and literal line breaks inside strings. All legal in JavaScript, all fatal in JSON — which is exactly why they slip through.

No — JSON is a stricter subset: keys must be double-quoted strings, no comments, no trailing commas, no undefined or functions. Every JSON document is a valid JS object literal; the reverse fails constantly.

The response is HTML, not JSON — usually an error page (404, 500, login redirect) where the parser expected data. Paste the raw response here: seeing <html at position 0 diagnoses it instantly.

No — by design (Douglas Crockford removed them to prevent parsing directives). Workarounds: a "_comment" key, or JSONC/JSON5 formats where tooling supports them (VS Code settings do; APIs don't).

Yes — validation runs entirely in your browser; nothing is uploaded or stored. Payloads with tokens and keys stay on your machine.