What is JSON?

JSON stands for JavaScript Object Notation. It is a lightweight, text-based format for storing and exchanging data between systems. Created by Douglas Crockford in 2001 and standardized as ECMA-404 and RFC 8259, JSON has become the de facto standard for web APIs — over 70% of public APIs use JSON. Unlike XML, it is human-readable and easy for both humans and machines to parse.

A JSON document is plain text. It contains key-value pairs wrapped in curly braces. Here is a simple example representing a user:

{
  "name": "Alice",
  "age": 30,
  "email": "[email protected]",
  "active": true,
  "roles": ["admin", "editor"],
  "address": {
    "city": "New York",
    "country": "US"
  }
}

Every key is a string in double quotes. Values can be strings, numbers, booleans, arrays, objects, or null. That is the entire type system.

Before JSON, XML was the dominant data exchange format for the web. XML is verbose — every value needs an opening and closing tag. Douglas Crockford noticed that JavaScript already had a natural object literal syntax, and he formalized it into a language-independent standard. The result is a format that is:

• Smaller than XML for the same data
• Readable without special tooling
• Natively parsed by every major programming language
• Trivial to generate from any data structure

JSON is everywhere in modern software:

• REST APIs — almost every web API returns JSON responses
• Configuration files — package.json, tsconfig.json, VS Code settings
• Databases — PostgreSQL, MySQL, and MongoDB store JSON natively
• Browser storage — localStorage and sessionStorage store JSON strings
• Message queues — Kafka, RabbitMQ payloads are often JSON
• Log files — structured logging commonly uses JSON lines

JSON is not the only option, but it is usually the best default:

• vs XML — JSON is 30–50% smaller for the same data and far easier to read
• vs CSV — CSV is great for flat tabular data but cannot represent nested structures
• vs YAML — YAML supports comments and is popular for config, but is whitespace-sensitive and error-prone
• vs MessagePack — MessagePack is a binary format that is faster and smaller, but not human-readable

For a deeper comparison, see JSON vs XML vs CSV.

No. JSON looks like a JavaScript object literal but is a string. The key differences:

• JSON keys must always be in double quotes — JavaScript allows unquoted keys
• JSON does not support functions, undefined, or Date objects
• JSON is language-independent — Python, Go, Java, and Rust all parse it natively

Paste any JSON into the JSON Formatter to instantly pretty-print and explore it. Run it through the JSON Validator to confirm it is syntactically correct before using it in your code.