JSON Validator: how to use it (and why it helps)

What this tool does

JSON (JavaScript Object Notation) is the format most APIs, config files, and data exports use. It's strict: a single misplaced comma or quote makes the whole document invalid. The JSON Validator checks your text against those rules and, when it's valid, pretty-prints a cleanly indented copy. It runs entirely in your browser using the same JSON parser your code uses, so the result matches what your program will see.

How to use it

1. Open the JSON Validator.
2. Paste or type your JSON into the Input box (or press Load sample to try it with example data).
3. Click Validate & format, or press Ctrl/Cmd + Enter while in the input box.
4. If it's valid, a formatted copy appears in the Output pane and the status line turns green. Use Copy to grab the result.
5. Choose the Indent (2 spaces, 4 spaces, or a tab) to match your project's style; the output re-formats instantly.

Reading the error messages

If the JSON is invalid, the status line turns red and tells you what went wrong and where — for example, line 3, column 3. The line and column point at the spot where the parser gave up, which is usually at or just after the real mistake. The most common culprits are:

• Trailing commas — [1, 2, 3,] is invalid; remove the last comma.
• Single quotes — JSON strings and keys must use double quotes (").
• Unquoted keys — { name: "x" } must be { "name": "x" }.
• Missing commas between array items or object properties.
• Comments — standard JSON does not allow // or /* */.

Why validating JSON is useful

Catching a malformed payload early saves a frustrating round of debugging later. Reaching for a validator pays off when you're:

• Debugging an API response that your code refuses to parse.
• Editing a package.json, tsconfig.json, or other config file by hand.
• Cleaning up minified JSON into something readable before review.
• Confirming that data copied between tools survived the trip intact.

Your data stays private

Everything happens locally in your browser — nothing you paste is uploaded to a server. That makes the tool safe to use with internal or sensitive payloads, and it's why it works instantly with no network round-trip.

FAQ

Is my JSON uploaded anywhere?

No. The validator uses your browser's built-in JSON parser; nothing leaves the page.

Why does valid-looking JSON fail?

Usually a trailing comma, a single quote, an unquoted key, or a stray comment. Jump to the reported line and column and check the characters just before it.

What's the difference between validating and formatting?

Validating confirms the syntax is correct; formatting re-indents valid JSON so it's easy to read. This tool does both in one step.

Ready to try it? Open the JSON Validator →