JSON Validator

How to use the JSON Validator

1. Paste JSON into the editor, or click Sample to see an example with mistakes.
2. The result updates as you type: "Valid JSON" with a structure summary, or the first error with its line and column.
3. The line with the error is highlighted in the editor, with a plain-English explanation and a hint.
4. For common mistakes you also get a suggested fix. Copy it, or click Use this to replace your input.

What it checks

Input is checked against the strict JSON standard (RFC 8259), the same rules used by JSON.parse, Java's Jackson, Python's json module and API gateways. Things that work in JavaScript but not JSON are reported as errors:

• Trailing commas, single-quoted strings and unquoted keys
• Comments
• undefined, NaN, Infinity, hex numbers and leading zeros
• Python-style True, False and None
• Missing commas, colons, brackets or braces, and unterminated strings

It also warns about duplicate keys. They're technically valid, but most parsers silently keep only the last value, which is a common source of configuration bugs.

Frequently asked questions

Is my JSON sent to a server?

No. Validation and repair run entirely in your browser. Nothing you paste is uploaded or stored.

Can it fix my JSON automatically?

It can suggest a fix for most common mistakes: quotes, trailing commas, comments, unquoted keys, missing commas and unclosed brackets. Always review the suggestion. Some fixes are guesses, and a few inputs can't be repaired at all.

Why does it only show one error?

After the first syntax error, a parser can't reliably tell what the rest of the document means, so later "errors" are often misleading. Fix the first one and the validator immediately checks again.

What's the difference between this and the JSON Formatter?

Both check your JSON. The validator focuses on finding and fixing problems and summarizing the structure. The formatter focuses on producing nicely indented or minified output.