JSON Tools

JSON Validator

Strict RFC 8259 validation with the exact line and column of every error — plus one-click repair for broken JSON.

In short

A JSON validator checks that a document follows RFC 8259: double-quoted keys and strings, correctly nested objects and arrays, and only the literals true, false and null. This validator does a full parse in your browser, reports the exact line and column of the first violation, marks it in the editor, and repairs common mistakes in one click.

By NaveenKumar T · Updated 18 Sep 2026

Learn: How to Fix Invalid JSON: Every Common Error, Decoded

Exact error line & column
Strict RFC 8259 parsing
One-click JSON repair

Runs entirely in your browser — nothing you paste or open here is uploaded, logged, or stored.How we handle data →

Example

JSON Validator: input and output

A complete, valid invoice — exactly the kind of document you'd run through Validate before it reaches an accounting API.

Input · json

{
  "invoice_id": "INV-2026-0745",
  "issued_on": "2026-07-01",
  "due_on": "2026-07-15",
  "customer": { "name": "Ada Lovelace", "email": "ada@example.com" },
  "line_items": [
    { "description": "Pro plan — August", "amount": 49.0 },
    { "description": "Extra seats (3)", "amount": 27.0 }
  ],
  "currency": "USD",
  "total": 76.0,
  "paid": false
}

Output · json

{
  "invoice_id": "INV-2026-0745",
  "issued_on": "2026-07-01",
  "due_on": "2026-07-15",
  "customer": {
    "name": "Ada Lovelace",
    "email": "ada@example.com"
  },
  "line_items": [
    {
      "description": "Pro plan — August",
      "amount": 49
    },
    {
      "description": "Extra seats (3)",
      "amount": 27
    }
  ],
  "currency": "USD",
  "total": 76,
  "paid": false
}

Look closely at the amounts: 49.0 and 76.0 come back as 49 and 76. JSON has no separate float type, so the serializer drops insignificant trailing zeros — the value is unchanged, only its printed form is.

Learn more

What does a JSON validator check?

A JSON validator verifies that a document conforms to the JSON specification: properly quoted keys and strings, correctly nested objects and arrays, legal number formats, and only the literals true, false, and null. This validator performs a full parse — the same operation your application will do — so if it passes here, JSON.parse and equivalent parsers in any language will accept it.

Unlike validators that just say 'invalid', this tool pinpoints the first violation with its exact line and column, both in the status bar and as a red marker inside the editor. For large API responses, that turns minutes of squinting into a single click. Syntax is only the first gate — to check that the document also has the right fields and types, validate it against a JSON Schema instead.

How to fix invalid JSON quickly

Start with Validate to locate the first error, fix it, and validate again — JSON parsers stop at the first violation, so errors are revealed one at a time. For documents that were hand-written in a JavaScript style (single quotes, trailing commas, comments), the Repair action fixes all of those mechanical issues at once.

If your document validates but looks wrong, the problem is usually structure rather than syntax: use the Tree view to inspect nesting, counts, and types at a glance, or the filter bar to query a specific path. The wrench here and the standalone JSON Repair tool run the same engine; the dedicated page additionally shows every edit it made.

Help

Frequently asked questions

Everything you need to know about the JSON Validator.

01How do I validate JSON online?

Paste your JSON into the input editor and click Validate. The document is parsed against the JSON specification (RFC 8259); if anything is wrong, the status bar reports the exact line and column, and the editor underlines the failing position so you can fix it immediately.

02What makes a JSON document invalid?

The most common violations are trailing commas after the last item, single quotes instead of double quotes, unquoted property names, comments (JSON has none), and special values like NaN, Infinity, or undefined. Control characters inside strings and mismatched brackets are frequent in machine-generated payloads.

03Can the validator fix my JSON automatically?

Yes — click the wrench icon (Repair). It converts single quotes to double quotes, removes trailing commas and comments, quotes bare keys, and completes truncated documents, then re-validates the result. Always review the repaired output before using it.

04Is my JSON uploaded anywhere during validation?

No. Validation runs entirely in your browser with JavaScript — nothing you paste is transmitted, logged, or stored. The page even works offline once loaded.

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