Is Your JSON Valid? How to Validate It

What makes JSON valid?

A JSON document is valid when it follows the rules of the JSON specification (RFC 8259). There are two levels of correctness:

• Syntax validity — the text is well-formed JSON: correct brackets, quoted keys, no trailing commas, no comments.
• Schema validity — the data has the expected structure: required fields exist, values have the right type, numbers are within allowed ranges.

A JSON parser validates syntax. JSON Schema validates structure. Both matter — but you need syntax to be valid first.

This site's JSON Formatter validates syntax live and points to the exact line where parsing fails.

Common JSON errors

These are the mistakes that most often break JSON documents:

JSON syntax rules — quick reference

Validate JSON in code

Every major language has a built-in JSON parser. Wrap the parse call in a try/catch to validate:

JavaScript / Node.js

javascripttry {
  const data = JSON.parse(str)
  console.log('Valid JSON', data)
} catch (e) {
  console.error('Invalid JSON:', e.message)
}

Python

pythonimport json

try:
    data = json.loads(s)
    print('Valid JSON', data)
except json.JSONDecodeError as e:
    print('Invalid JSON:', e)

PHP

php$data = json_decode($str, true);
if (json_last_error() !== JSON_ERROR_NONE) {
    echo 'Invalid JSON: ' . json_last_error_msg();
}

Go further with JSON Schema

Syntax validation only checks that the JSON is parseable. JSON Schema lets you validate the content — required fields, value types, formats, and ranges.

example JSON Schema{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "required": ["name", "age", "email"],
  "properties": {
    "name":  { "type": "string", "minLength": 1 },
    "age":   { "type": "integer", "minimum": 0, "maximum": 150 },
    "email": { "type": "string", "format": "email" }
  }
}

With this schema, {"name": "Jane", "age": -5, "email": "jane@example.com"} would fail validation because age is below the minimum of 0 — even though it's perfectly valid JSON syntax.