What is JSON?

JSON stands for JavaScript Object Notation. It is a lightweight, text-based data interchange format that is easy for humans to read and write, and easy for machines to parse and generate. Despite its name, JSON is language-independent and is supported by virtually every modern programming language.

History

JSON was developed by Douglas Crockford in the early 2000s as a simpler alternative to XML for transmitting data between a server and a web application. It was first described in 2001 and later standardized as ECMA-404 and RFC 8259. Today it is the dominant format for web APIs and configuration files worldwide.

Basic Syntax

A JSON value is either an object, an array, a string, a number, a boolean, or null. An object is a set of key-value pairs enclosed in curly braces, where keys must be strings in double quotes. An array is an ordered list of values enclosed in square brackets.

{
  "name": "Alice",
  "age": 30,
  "active": true,
  "score": 9.5,
  "tags": ["developer", "designer"],
  "address": {
    "city": "Istanbul",
    "country": "Turkey"
  },
  "nickname": null
}

Data Types

JSON supports exactly six value types:

• String — Text in double quotes: "Hello, World!"
• Number — Integer or floating-point: 42, 3.14, -7
• Boolean — true or false
• Null — An empty value: null
• Object — A collection of key-value pairs: {"key": "value"}
• Array — An ordered list of values: [1, "two", true]

Common Use Cases

• Web APIs — REST APIs return JSON that browsers and apps parse natively
• Configuration files — Node.js (package.json), VS Code, and many other tools use JSON for settings
• Databases — NoSQL databases such as MongoDB and Elasticsearch store data in JSON format
• Data exchange — Services communicate by sending JSON payloads over HTTP
• Local storage — Browsers store structured data as JSON strings via localStorage

JSON vs XML

Before JSON, XML was the dominant format for data exchange. JSON has largely replaced XML in web development because:

• JSON syntax is shorter and easier to read
• JSON maps directly to native data structures in most languages
• JSON requires less bandwidth and parses faster
• JSON is natively supported in JavaScript without any additional library

XML is still preferred when document structure, namespaces, comments, or schemas (XSD) are required.

Rules to Remember

• Keys must always be double-quoted strings — single quotes are not valid
• Trailing commas are not allowed
• Comments are not part of the JSON standard
• Numbers cannot have leading zeros (except 0 itself)
• NaN and Infinity are not valid JSON values