Free Online JSON Validator

What is a JSON Validator?

A JSON validator is a specialized tool that checks whether a given text string conforms to the JSON (JavaScript Object Notation) standard. It performs syntax verification to ensure the JSON data is well-formed, properly structured, and can be reliably parsed by any standard-compliant JSON parser.

How JSON Validation Works

JSON validation involves a precise parsing process that follows these steps:

1. Lexical analysis of the input string to recognize tokens (strings, numbers, keywords, punctuation)
2. Syntactic analysis to verify the structure follows JSON grammar rules
3. Verification of proper nesting for objects and arrays
4. Confirmation that all opening brackets, braces, and quotes have matching closing pairs
5. Validation that all property names are properly quoted with double quotes
6. Checking that values conform to valid JSON data types (string, number, object, array, boolean, null)
7. Verification that all elements are properly separated by commas without trailing commas

When errors are detected, our validator pinpoints their exact location with line and column numbers, along with a clear explanation of the issue, making debugging straightforward.

Key Features of Our JSON Validator

• Real-time validation with immediate feedback as you type
• Precise error location highlighting with line and column indicators
• Descriptive error messages that explain the exact problem
• Syntax highlighting that makes JSON structure visually clear
• Support for large JSON files with efficient parsing
• Detection of common JSON errors like missing quotes, invalid escape sequences, and improper nesting
• Ability to handle and validate complex, deeply nested JSON structures
• Optional auto-formatting of valid JSON for improved readability
• Client-side processing for privacy (your data never leaves your browser)
• Dark and light mode visual themes

Common Use Cases

• Validating API request and response payloads before processing
• Debugging issues with malformed JSON data
• Verifying configuration files during development and deployment
• Ensuring data interchange formats are standards-compliant
• Checking user-submitted JSON inputs for validity
• Learning proper JSON syntax through immediate feedback
• Testing output from JSON generation tools and exports
• Validating stored JSON data before database operations
• Ensuring webhook payloads are correctly formatted

JSON Standards and Best Practices

• Adhere to RFC 8259: Follow the official JSON specification (ECMA-404 and RFC 8259)
• Validate Early: Check JSON validity before attempting to parse or process it
• Use Try-Catch: When parsing JSON programmatically, always use error handling
• Consistent Property Naming: Use a consistent convention for property names (camelCase or snake_case)
• Use JSON Schema: For complex data, define a JSON Schema to validate structure beyond syntax
• Include Required Fields: Ensure all required fields are present in your JSON
• Appropriate Types: Use the most appropriate data type for each value (number vs. string)
• ISO Date Format: Use ISO 8601 format for dates (YYYY-MM-DDTHH:mm:ss.sssZ)
• Reasonable Nesting: Avoid excessively deep nesting of objects and arrays
• Minimize Size: For production, consider minifying JSON to reduce size

JSON Limitations and Common Errors

Being aware of JSON's limitations can help avoid common validation errors:

• No Comments: JSON doesn't support comments, unlike JavaScript
• Double Quotes Only: Property names and strings must use double quotes, not single quotes
• No Trailing Commas: JSON doesn't allow commas after the last element in arrays or objects
• Limited Data Types: Only strings, numbers, objects, arrays, booleans, and null are valid
• No Special Values: NaN, Infinity and undefined are not valid in JSON
• No Circular References: JSON can't represent objects that reference themselves
• Date Formatting: Dates must be stored as strings, typically in ISO format
• Control Characters: Certain characters in strings must be properly escaped

{
  "name": "Smart Thermostat",
  "price": 129.99,
  "isAvailable": true,
  "features": ["Wi-Fi", "Voice Control", "Energy Reports"],
  "specifications": {
    "dimensions": "3.4 × 3.4 × 1.2 inches",
    "weight": "8.8 ounces",
    "warranty": "2 years",
    "compatibility": null
  }
}

{
  name: "Smart Thermostat",        // Error: Unquoted property name
  'price': 129.99,                 // Error: Single quotes instead of double
  isAvailable: true,               // Error: Unquoted property name
  features: ["Wi-Fi", "Voice Control", "Energy Reports",],  // Error: Trailing comma
  // This is a comment                // Error: Comments not allowed in JSON
  specifications: {
    "dimensions": "3.4 × 3.4 × 1.2 inches",
    "weight": "8.8 ounces",
    "warranty": undefined           // Error: undefined is not valid in JSON
  },
}