TOOLADEX

JSON Validator

Validate JSON syntax instantly. Check if your JSON is valid, find errors with precise location information, and get detailed feedback. Perfect for debugging API responses, configuration files, and data validation.

100% Client-Side Processing

Your JSON is validated entirely in your browser. No data is sent to any server.

Common JSON Errors

❌ Trailing Commas

JSON doesn't allow commas after the last item in objects or arrays.

{
  "key": "value",
}

❌ Unquoted Keys

All object keys must be wrapped in double quotes.

{
  key: "value"
}

❌ Single Quotes

JSON only supports double quotes for strings.

{
  "key": 'value'
}

❌ Comments

JSON doesn't support comments (unlike JavaScript).

{
  // This is a comment
  "key": "value"
}

Table of Contents

What is JSON Validation?

JSON validation is the process of checking whether a JSON string conforms to the JSON specification. A valid JSON string must follow strict syntax rules, and any deviation from these rules will cause parsing to fail.

Unlike JavaScript objects, JSON has a more restrictive syntax:

  • All keys must be in double quotes
  • Strings must use double quotes (single quotes are not allowed)
  • No trailing commas in objects or arrays
  • No comments
  • No undefined values (use null instead)
  • No functions or other JavaScript-specific features

Validating JSON before using it in your application helps prevent runtime errors and ensures your data structures are correctly formatted.

Common JSON Errors

Trailing Commas

One of the most common mistakes is adding a comma after the last item in an object or array. While this is valid in JavaScript, it's not allowed in JSON.

❌ Invalid

{
  "name": "Alice",
  "age": 30,
}

✅ Valid

{
  "name": "Alice",
  "age": 30
}

Unquoted Keys

In JavaScript, object keys don't need quotes if they're valid identifiers. In JSON, all keys must be strings wrapped in double quotes.

❌ Invalid

{
  name: "Alice",
  age: 30
}

✅ Valid

{
  "name": "Alice",
  "age": 30
}

Single Quotes for Strings

JSON only supports double quotes for strings. Single quotes are not valid JSON syntax.

❌ Invalid

{
  "message": 'Hello, world!'
}

✅ Valid

{
  "message": "Hello, world!"
}

Comments

JSON doesn't support comments, even though many developers expect this feature (it exists in JSON5 and JSONC).

❌ Invalid

{
  // This is a comment
  "key": "value"
}

✅ Valid

{
  "key": "value"
}

Use Cases

  • API Development: Validate API responses before processing them in your application
  • Configuration Files: Check configuration files like package.json, tsconfig.json, or custom config files for syntax errors
  • Data Import: Validate JSON data before importing it into databases or applications
  • Debugging: Quickly identify syntax errors in JSON received from external sources
  • Code Reviews: Validate JSON files before merging code changes
  • Testing: Ensure test data is valid JSON before running tests
  • Learning: Understand JSON syntax rules and common mistakes

Best Practices

Validate Before Processing

Always validate JSON before attempting to process it in your application. Use try-catch blocks when parsing JSON to handle validation errors gracefully.

Use a JSON Validator Tool

For large or complex JSON, use a validator tool (like this one) to quickly identify syntax errors before debugging in your application code.

Validate API Responses

When working with APIs, validate the JSON responses to ensure they're well-formed before processing. This helps catch issues early in development.

Check Configuration Files

Validate configuration files regularly, especially after manual edits. A single syntax error can prevent your application from starting.

Use Schema Validation for Complex Data

While syntax validation ensures JSON is well-formed, consider using JSON Schema validation to ensure the data structure and values meet your requirements.

Frequently Asked Questions

What's the difference between JSON validation and JSON formatting?

JSON validation checks if JSON syntax is correct and well-formed. JSON formatting (also called "pretty printing") adds indentation and line breaks to make JSON more readable. This tool focuses on validation, while our JSON Formatter tool handles formatting.

Can this tool validate JSON Schema?

No. This tool validates JSON syntax only. JSON Schema validation is a separate process that checks if JSON data conforms to a predefined schema structure. Schema validation is a future enhancement we're considering.

Why does my JSON show as invalid?

Common reasons include trailing commas, unquoted keys, single quotes instead of double quotes, comments, or syntax errors like mismatched brackets. Check the error message for the specific issue and its location.

Can I validate very large JSON files?

This tool works in your browser, so very large files (hundreds of MBs) may cause performance issues. For extremely large files, consider using command-line tools or server-side validation. Most typical JSON files work fine.

Is my JSON data sent to a server?

No. All validation happens entirely in your browser using JavaScript. Your JSON never leaves your device. This tool is designed with privacy as a top priority.

What does the error position mean?

The error position indicates where in your JSON the error was detected. Line and column numbers help you quickly locate the problematic code. However, note that some errors may be detected slightly after the actual problem (e.g., a missing quote may be detected when parsing continues).

Can I validate JSON with comments or single quotes?

No. Standard JSON doesn't support comments or single quotes. If you have JSON with these features, you're likely working with JSON5 or JavaScript object syntax, which needs to be converted to valid JSON first.