What Is JSON? A Beginner’s Guide

JSON stands for JavaScript Object Notation. It’s a lightweight, text-based format for storing and exchanging structured data, and it’s become the standard way most modern applications send data back and forth.

What Does JSON Stand For?

JSON stands for JavaScript Object Notation. The name comes from the fact that its syntax is based on how objects are written in JavaScript. Despite the name, JSON isn’t tied to JavaScript: it’s a plain text format that almost every modern programming language can read and write, including Python, PHP, Java, Ruby, and Go.

What Does JSON Look Like?

Here’s a simple JSON object describing a person:

{
  "name": "John",
  "age": 30,
  "city": "London"
}

This is an object, shown by the curly braces { }. Inside it are three key-value pairs. Each key (like "name") is a label written in double quotes, followed by a colon and its value (like "John"). Pairs are separated by commas.

JSON Data Types

JSON supports a small, fixed set of value types:

• String: text wrapped in double quotes, e.g. "London"
• Number: written without quotes, e.g. 30
• Boolean: either true or false
• Array: an ordered list of values in square brackets
• Object: a set of key-value pairs in curly braces
• null: represents an intentionally empty value

JSON Objects and Arrays

An object groups related values under named keys. An array is an ordered list of values, written in square brackets and separated by commas:

["Apple", "Banana", "Orange"]

Objects and arrays can be combined and nested inside each other. Here’s a more realistic example:

{
  "name": "John",
  "age": 30,
  "isEmployed": true,
  "address": {
    "city": "London",
    "postcode": "E1 6AN"
  },
  "hobbies": ["reading", "cycling", "chess"]
}

Here, address is an object nested inside the outer object, and hobbies is an array of strings. Nesting is what lets JSON represent complex, real-world data.

JSON Syntax Rules

• Keys must be strings, written in double quotes (not single quotes).
• String values must also use double quotes.
• Commas separate items, but standard JSON does not allow a trailing comma after the last item in an object or array.
• Numbers, true, false, and null are written without quotes.
• Every opening brace or bracket needs a matching closing one.

Breaking any of these rules produces invalid JSON that most parsers will reject.

Where Is JSON Used?

• APIs: most web APIs send and receive data as JSON.
• Web applications: browsers and servers exchange JSON behind the scenes.
• Configuration files: many tools and frameworks store settings as JSON.
• Data storage: some databases store records directly as JSON documents.
• JavaScript applications: JSON maps directly onto JavaScript objects, making it a natural fit.

JSON vs XML

Before JSON became dominant, XML was the standard format for exchanging structured data. Both can represent the same information:

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

<person>
  <name>John</name>
  <age>30</age>
</person>

JSON is generally more compact and easier to read at a glance, which is part of why it overtook XML for most web APIs. XML supports some things JSON doesn’t natively, like attributes and comments, and is still common in document formats and older enterprise systems. Neither format is universally “better”: the right choice depends on what a system already uses and needs.

How to Validate and Format JSON

Hand-written JSON is easy to get wrong: a missing comma or an extra bracket is enough to break it. The JSON Formatter & Validator checks your JSON for syntax errors and points out exactly where the problem is, and can also reformat cramped or minified JSON into a readable, indented layout. If you’re moving data between formats, the JSON to CSV Converter and CSV to JSON Converter tools convert JSON and CSV in either direction.

JSON often shows up alongside other data-handling concepts. If your data needs to travel through binary-unsafe channels, see What Is Base64 Encoding?; if it’s being placed into a URL, see What Is URL Encoding?; and if you need to search or validate JSON string values, see Regex Explained for Beginners.