What is JSON?
A plain-English guide to JSON — with a live formatter to practice.
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JSON in plain English
JSON (JavaScript Object Notation) is a text format for storing and exchanging structured data. It's the most widely used data format on the web — almost every API, config file, and database uses it.
Think of JSON like a dictionary: it stores information as labelled pairs. The label (key) tells you what the information is; the value tells you the actual data.
{
"firstName": "Alice",
"age": 30,
"isActive": true,
"scores": [95, 87, 92],
"address": {
"city": "Auckland",
"country": "New Zealand"
}
}
JSON syntax rules (all of them)
- Data is in key-value pairs:
"key": value - Keys must be strings in double quotes
- String values must be in double quotes (not single quotes)
- Objects are wrapped in
{} - Arrays are wrapped in
[] - Values can be: string, number, boolean, null, object, or array
- Items are separated by commas — no trailing comma after the last item
- No comments allowed
Why JSON won: It's human-readable, language-independent, and lighter than XML. Before JSON (circa 2006), XML was dominant for data exchange — JSON replaced it almost everywhere because it's simpler to write and parse.
Frequently asked questions
JSON stands for JavaScript Object Notation. Despite the JavaScript in the name, JSON is language-independent — every major programming language has built-in JSON support.
The main uses: API data exchange (sending and receiving data between web services), configuration files (package.json, .eslintrc, tsconfig.json), database storage (PostgreSQL JSONB columns, MongoDB documents, DynamoDB), and local data storage in browsers (localStorage).