How to Validate JSON and Fix Common Errors

A single misplaced comma can break an entire API request or crash a config load. JSON is strict — stricter than most people remember — and the error messages parsers give are often unhelpful. A validator checks your JSON against the specification and tells you exactly where and why it fails. This guide covers the rules JSON actually enforces, the errors that trip everyone up, and how to fix them fast.

What validation checks

Validating confirms that your text is legal JSON: every bracket and brace is matched and closed, strings use double quotes, keys and values are properly separated, and there are no illegal trailing commas. If anything is off, the validator points to the location so you are not hunting blind.

How to validate JSON with this tool

1. Open the JSON Validator tool.
2. Paste your JSON.
3. Read the result — valid, or an error with its position.
4. Fix and re-check.

Everything runs in your browser, so sensitive data is never uploaded.

The errors that catch everyone

JSON's rules are simple but unforgiving. The usual offenders:

• Trailing commas. A comma after the last item in an array or object is illegal in JSON, even though JavaScript allows it. This is the single most common mistake.
• Single quotes. JSON requires double quotes for both keys and string values. `'name'` is invalid; `"name"` is correct.
• Unquoted keys. Object keys must be quoted strings. `{name: "x"}` fails; `{"name": "x"}` passes.
• Missing commas between items, or a stray comma where none belongs.
• Comments. Standard JSON does not allow `//` or `/* */` comments at all.
• Unescaped characters inside strings, like a raw newline or an unescaped quote.

Why not just rely on your code?

By the time your application throws a JSON error, it is mid-crash and the message is usually generic ("unexpected token"). Validating the raw text first isolates the problem cleanly, before it reaches your code, and shows the precise character at fault.

Format while you fix

Pasting messy JSON into JSON Formatter makes structural errors visually obvious — indentation exposes an unclosed brace instantly. Validate to find the error, format to see it in context. Once clean, JSON to CSV or JSON to YAML can transform it.

Common uses

• Check a config file before deploying.
• Verify an API payload you hand-edited.
• Debug an "invalid JSON" error in your app.

Privacy and limits

Validation is fully local — no upload, no size cap, nothing stored, offline once loaded. Open the JSON Validator tool to catch errors before they break something.