How to Use JSON Validator

Key Takeaways

Validator checks whether JSON is syntactically correct and reports errors with line numbers

Trailing commas (not allowed in JSON), single quotes instead of double quotes, unquoted keys, missing commas between items, and unterminated strings

The validator checks strict JSON (RFC 8259)

JavaScript eval() and JSON

What is JSON Validator?

JSON Validator checks whether a JSON string is syntactically valid according to the JSON specification (RFC 8259), reports the exact line and column of any error, and explains what went wrong — so you fix it in seconds instead of scanning hundreds of lines manually.

A single misplaced comma or missing quote breaks an entire JSON document. The validator finds it immediately so you don’t waste time searching by eye.

Common JSON Errors

Trailing Comma

JSON does not allow a comma after the last item in an object or array. JavaScript does; JSON doesn't.

Single Quotes

JSON requires double quotes for strings and keys. Single quotes are a JavaScript-only extension.

Unquoted Keys

Object keys must always be in double quotes: {"key": "value"} not {key: "value"}.

Missing Comma

Every item in an array or object must be separated by a comma except the last.

Undefined / NaN

JSON only supports null, not JavaScript's undefined or NaN. These must be replaced with null or removed.

Paste your JSON

Paste any JSON string into the input field — API response, config file, or data payload.

→

Validate instantly

A green badge means valid JSON. A red badge shows the first error with line number.

→

Read the error

The error message explains what's wrong: 'Unexpected token' or 'Expected comma after value'.

→

Fix and revalidate

Edit the JSON in place and the validator updates immediately as you type.

Valid vs Invalid Examples

Invalid (trailing comma):

{
  "name": "Alice",
  "age": 30,
}

Valid:

{
  "name": "Alice",
  "age": 30
}

Tips & Common Mistakes

Validate API responses during development. Paste the raw response body here before writing code to parse it. You’ll catch unexpected nulls, type mismatches, and malformed data before they cause runtime errors.

Copy from browser DevTools carefully. When copying a network response from Chrome DevTools, the preview panel sometimes adds formatting artifacts. Always copy from the “Response” tab, not “Preview.”

Don’t confuse JSON with JavaScript objects. JavaScript object literals allow unquoted keys, trailing commas, and single quotes. JSON does not. If you’re writing a config file that needs these features, consider JSON5 or YAML instead.

JSON Formatter — pretty-print valid JSON with indentation
JSON to CSV — convert validated JSON to a spreadsheet
JSON to XML — convert JSON to XML format

Frequently Asked Questions

What is the difference between JSON Validator and JSON Formatter?

Validator checks whether JSON is syntactically correct and reports errors with line numbers. Formatter pretty-prints valid JSON with indentation. Use Validator first if you're unsure if your JSON is valid.

What are the most common JSON errors?

Trailing commas (not allowed in JSON), single quotes instead of double quotes, unquoted keys, missing commas between items, and unterminated strings.

Is JSON5 supported?

The validator checks strict JSON (RFC 8259). JSON5 extensions like comments, trailing commas, and single quotes are flagged as errors — which is correct for standard JSON.

Why does my JSON work in JavaScript but fail here?

JavaScript eval() and JSON.parse() in some environments are lenient about trailing commas and other extensions. Strict JSON validators follow the spec — which is what most APIs and parsers expect.

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How to Use JSON Validator — Complete Guide