What are the strict syntax rules of RFC 8259 JSON?

In standard JSON: (1) all object keys must be wrapped in double quotes (`"name"`), (2) all string values must use double quotes (never single quotes), (3) trailing commas after the last element in an object or array are forbidden, (4) comments (`//` or `/* */`) are not allowed, and (5) numbers cannot have leading zeros (like `01`).

How do I include a double quote or newline inside a JSON string?

You must escape them with a backslash: use `\"` for a literal double quote inside a string, `\n` for a line break, `\t` for a tab, and `\\` for a literal backslash.

Are `undefined` or `NaN` valid values in JSON?

No. Standard JSON only supports six data types: Object (`{}`), Array (`[]`), String (`""`), Number (`42`, `3.14`), Boolean (`true`, `false`), and `null`. JavaScript values like `undefined`, `NaN`, `Infinity`, and functions are rejected by JSON parsers.

Does this tool validate against a JSON Schema?

This tool validates RFC 8259 syntax and structural well-formedness, ensuring `JSON.parse()` will succeed in any programming language.

Is my JSON data sent over the internet?

Never. Validation executes 100% locally in your browser's JavaScript engine.

JSON Validator Online — Check RFC 8259 JSON Syntax Live

Paste JSON to check

The result appears as soon as you paste something.

How to Use the JSON Validator

1
Paste or type the JSON document you want to test into the validator editor.
2
Inspect the live status banner immediately below the editor (Valid JSON in green, or Invalid JSON with the parser error message).
3
Edit any broken quotes, missing commas, or unescaped characters right in the box until the banner turns green.
4
Optionally jump to the JSON Formatter to beautify or minify your verified payload.

Practical Use Cases

Software Developers

Debugging Config Files & Webhook Payloads

Catch missing commas, mismatched curly braces, and unescaped quotes in `package.json`, IAM policy documents, and REST request bodies.

Data & Analytics Teams

Validating JSON Exports Before Database Ingestion

Verify that generated JSON data feeds parse cleanly before importing into MongoDB, BigQuery, PostgreSQL `jsonb` columns, or Elasticsearch.

Students & API Integrators

Learning Strict RFC 8259 JSON Rules

Test how standard JSON parsers handle numbers, booleans, nested arrays, and escaped Unicode strings.

JSON Validator Features

Zero-Click Live Validation

Runs native parser validation immediately as you paste or edit characters.

Structural Summary Readout

Displays top-level type (Object/Array), item/key count, and character length when valid.

Pinpoint Error Diagnostics

Shows the exact parser exception message and position when syntax is invalid.

Runs 100% in your browser

Nothing is uploaded to a remote server, so your data and files stay strictly on your device.

Free and unlimited

No account registration, no watermarks, and no daily usage caps.

Mobile and desktop ready

Responsive layouts and comfortable touch controls that fit phones, tablets, and desktops.

Technical Specifications & Best Practices

✓Enforces strict RFC 8259 / ECMA-404 JSON compliance — standard JSON does not permit comments (`//`), trailing commas, `undefined`, `NaN`, or single-quoted strings.
✓Reports top-level data type (Object with key count, Array with item count, or primitive) as soon as validation passes.
✓Validates syntax in real time with zero button clicks required.
✓100% client-side — your IAM policies, database rows, and API payloads never leave your browser.

JSON Validator