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Free JSON Validator

Paste JSON to check whether it is valid. If it isn't, you get the error plus the line and column where it breaks; if it is, you get a clean formatted copy.

✓ Valid JSON

Validates against the JSON standard (RFC 8259) in your browser — nothing is uploaded.

Quick answer

To validate JSON, parse it against the JSON standard (RFC 8259) and report the first place it breaks. This tool does that live as you type: it shows 'Valid JSON' or the exact error with its line and column, and pretty-prints anything that parses. Everything runs in your browser, so your data is not uploaded.

Formula & method

The tool runs your text through the browser's strict JSON parser. JSON requires double-quoted keys and strings, no trailing commas, no comments, and no single quotes — the most common reasons valid-looking text fails. When parsing throws, the tool converts the error's character position into a line and column so you can find the problem fast.

Examples

Example 1: Trailing comma
Input
{"a":1,}
Result
Invalid — near line 1, column 8
Why
JSON does not allow a comma before a closing brace or bracket.
Example 2: Single quotes
Input
{'a':1}
Result
Invalid JSON
Why
Keys and strings must use double quotes in JSON, not single quotes.
Example 3: Valid object
Input
{"a":1,"b":[2,3]}
Result
Valid JSON
Why
Parses cleanly and is pretty-printed for you.

When to use this tool

  • Debugging an API response or config file that won't parse.
  • Checking JSON before pasting it into code or another tool.
  • Finding the exact line and column of a syntax error.

Common mistakes

  • Trailing commas after the last item — valid in JavaScript, invalid in JSON.
  • Using single quotes instead of double quotes for keys or strings.
  • Adding // or /* */ comments, which JSON does not support.

Frequently asked questions

What is the difference between this and the JSON formatter?

The validator focuses on telling you whether JSON is valid and pinpointing the error's line and column. The JSON Formatter focuses on prettifying and minifying valid JSON. Both run in your browser.

Is my JSON uploaded?

No. Validation happens entirely in your browser, so your data never leaves your device.

Why is my JSON invalid when it looks fine?

The usual culprits are a trailing comma, single quotes instead of double quotes, comments, or an unquoted key — all common in JavaScript but not allowed in JSON.

Which JSON standard does it check?

It uses the browser's built-in parser, which follows the JSON standard (RFC 8259 / ECMA-404).

Can it fix the JSON for me?

It can't guess your intent, but it shows exactly where the error is so you can fix it, and it pretty-prints the result once it is valid.

Does it handle large JSON?

Yes, within your browser's memory. Very large files (tens of MB) may be slow because everything runs locally.

Sources & references

External references open in a new tab. We are independent and not affiliated with these organizations.

  • ✓ Free to use
  • ✓ No sign-up required
  • ✓ Runs entirely in your browser — nothing is uploaded.
  • ✓ Formula and method shown above
Last updated: How we calculateReport a correctionDisclaimer

Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.

Built and reviewed by HIFreeTools against the formula shown above and any authoritative references cited on this page. See our methodology and editorial standards.

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