JSON Validator

Validates a JSON string against RFC 4627 (The application/json media type for JavaScript Object Notation) and against the JavaScript language specification. You can configure the validator to be lenient or strict.

There is no limit to the file you can upload but be patient with big or huge files.

If you want to learn more about JSON, jump to the JSON Explained section of this page.

Option 1: Copy-paste your JSON string here
Option 2: Or type in the URL to your JSON file

The default validation occurs against the strict RFC 4627 specification which requires for names / keys to be in double quotes. E.g.: {example:"value"} is invalid but {"example":"value"} is valid. Use the following options for a lenient validator.

Accept non-quoted names Accept single-quotes Accept 'NaN' values Accept leading zeroes

JSON Explained

What is JSON?

JSON stands for "JavaScript Object Notation" and is pronounced "Jason" (like in the Friday the 13th movies). It's meant to be a human-readable and compact solution to represent a complex data structure and facilitate data-interchange between systems.

Why use JSON?

There are tons of reasons why you would want to use JSON:

  • It's human readable... if it's properly formatted :-P
  • It's compact because it doesn't use a full markup structure, unlike XML
  • It's easy to parse, especially in JavaScript
  • A gazillion JSON libraries are available for most programming languagues
  • The data structure is easy to understand even if you're an idiot

The JSON format

There are just a few rules that you need to remember:

  • Objects are encapsulated within opening and closing brackets { }
  • An empty object can be represented by { }
  • Arrays are encapsulated within opening and closing square brackets [ ]
  • An empty array can be represented by [ ]
  • A member is represented by a key-value pair
  • The key of a member should be contained in double quotes. (JavaScript does not require this. JavaScript and some parsers will tolerate single-quotes)
  • Each member should have a unique key within an object structure
  • The value of a member must be contained in double quotes if it's a string (JavaScript and some parsers will tolerates single-quotes)
  • Boolean values are represented using the true or false literals in lower case
  • Number values are represented using double-precision floating-point format. Scientific notation is supported
  • Numbers should not have leading zeroes
  • "Offensive"" characters in a string need to be escaped using the backslash character
  • Null values are represented by the null literal in lower case
  • Other object types, such as dates, are not properly supported and should be converted to strings. It becomes the responsability of the parser/client to manage this.
  • Each member of an object or each array value must be followed by a comma if it's not the last one
  • The common extension for json files is '.json'
  • The mime type for json files is 'application/json'
   "anObject": {
      "numericProperty": -122,
      "stringProperty": "An offensive \" is problematic",
      "nullProperty": null,
      "booleanProperty": true,
      "dateProperty": "2011-09-23"
   "arrayOfObjects": [
         "item": 1
         "item": 2
         "item": 3
   "arrayOfIntegers": [

JSON in JavaScript

Because JSON derives from JavaScript, you can parse a JSON string simply by invoking the eval() function. The JSON string needs to be wrapped by parenthesis, else it will not work! This is the #1 problem when programmers first start to manipulate JSON strings.

Example: <script type="text/language">

   // A valid json string
   var someJsonString = '{"someProperty":"someValue"}';

   // jsonObject will contain a valid JavaScript object
   var jsonObject = eval('(' + someJsonString + ')');

   // Will display the string 'someValue'


You can create JavaScript objects using the JSON syntax directly in your code.

Example: <script type="text/language">

   // jsonObject is a valid JavaScript object that can be used on the fly
   var jsonObject = { someProperty : "someValue" };

   // Will display the string 'someValue'


Programming languages and JSON

The website JSON.org maintains an extensive list of JSON libraries and they are categorized in programming languages. Unfortunately, there are so many libraries out there that it's very hard to chose one! Note that VERY few JSON libraries have strict adherence to the JSON specification and this can lead to parsing problems between systems.

These are my recommended JSON libraries:

Other useful JSON resources

  • JSON.org - Excellent overall explanation and list of many JSON libraries
  • Wikipedia - Brief explanation of JSON
  • TheServerSide.net - A list of JSON resource guide on TheServerSide.com