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"JSON Validator":{ }

Paste JSON or open a .json file to check it against the strict JSON standard (RFC 8259). Get an instant Valid or Invalid verdict, with the exact line and column of the first error and a caret pointing right at it. Runs 100% in your browser: zero network requests, so your data never leaves the page.

What is a JSON validator?

A JSON validator (also called a JSON checker) checks whether a block of text is valid JSON, and, when it isn't, tells you exactly where it breaks. This one parses your input against the strict JSON standard (RFC 8259) and reports the first error with its precise line and column, plus a caret pointing at the offending character. Valid input gets a green badge and a quick structure summary (root type, number of keys or items, total nodes, nesting depth, and size) so you can confirm you validated what you expected. It runs entirely in your browser, so config files, API responses, and payloads with secrets never leave your machine.

Common reasons JSON is invalid

  • Single quotes: JSON requires double quotes for keys and strings; 'value' is invalid.
  • Trailing commas: a comma before a closing } or ] is not allowed (that's JSON5, not JSON).
  • Comments: // and /* */ are not part of JSON.
  • Unquoted keys: every object key must be a double-quoted string.
  • Python-style literals: True, False, and None must be true, false, and null.
  • NaN / Infinity: not valid JSON numbers.
  • Trailing content: a stray character after the top-level value (a common copy-paste mistake).

Validate vs. repair

Validation is deliberately strict: it reports what a strict parser (browser, backend, or API) will actually reject, so it's the right check before you ship. Repair is the opposite. It rewrites non-standard input into clean JSON. When your text is only non-standard (single quotes, trailing commas, comments, Python literals) rather than genuinely broken, this validator flags it as repairable and links you to the JSON Formatter, which fixes it automatically. Use the validator to catch problems; use the formatter to fix the easy ones.

How to use

  1. Paste JSON into the Input pane, or click Open JSON file to load a .json file from your computer.
  2. The verdict updates as you type: a green Valid JSON badge, or a red Invalid JSON badge with the exact line and column.
  3. When invalid, read the message and the caret that points at the offending character, then fix it in place.
  4. When valid, check the structure summary (root type, keys/items, node count, depth, size) and copy the clean, formatted output.
  5. If the input is only non-standard (single quotes, trailing commas, comments), the validator links you to the Formatter to auto-repair it.

Examples

Valid JSON

Input
{ "name": "Ada", "roles": ["admin", "editor"] }
Output
✓ Valid JSON
Root: object · 2 keys · Depth: 2

Missing value

Input
{
  "a": 1,
  "b": 
}
Output
✗ Invalid JSON
Line 4, col 1: Unexpected token '}', expected a value

Trailing comma (non-standard)

Input
{ "a": 1, "b": 2, }
Output
✗ Invalid JSON. Line 1, col 17.
Repairable: the Formatter can auto-fix it.

FAQ

How do I validate JSON online?

Paste your JSON (or open a .json file) into the Input pane. The validator checks it against the strict JSON standard (RFC 8259) as you type and shows a Valid or Invalid verdict instantly. Everything runs in your browser. Nothing is uploaded.

Is this a JSON checker?

Yes. "JSON checker", "JSON validator", and "check if JSON is valid" all describe the same task: confirming that a block of text is valid JSON. This tool does exactly that, strictly (RFC 8259) and instantly, entirely in your browser.

Is my JSON sent to a server?

No. This validator is 100% client-side. Open DevTools → Network and confirm: zero requests after the page loads. Your data, including anything with tokens or personal information, never leaves your machine.

What does "valid JSON" mean?

Valid JSON follows RFC 8259: double-quoted keys and strings, no trailing commas, no comments, and only the literals true, false, and null. NaN and Infinity are not valid JSON values. This tool checks all of that strictly.

Why is my JSON invalid when it looks fine?

The most common causes are single quotes instead of double quotes, a trailing comma before } or ], an unquoted key, a comment, or Python-style True/False/None. The validator points at the exact line and column so you can spot it. If the input is repairable, it links you to the Formatter.

Does the validator fix my JSON?

No. Validation is strict on purpose, so you see real errors. When the input is merely non-standard, the tool tells you it is repairable and links to the JSON Formatter, which auto-fixes single quotes, trailing commas, comments, and Python-style literals.

Can it validate a large JSON file?

Yes. Paste it or open the file directly; parsing runs locally in your browser. For very large documents the JSON Viewer's collapsible tree is the easiest way to explore what you validated.

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