What Is JSON? A Complete Explanation of JavaScript Object Notation
Quick Answer
JSON is a text format for representing structured data using key-value pairs and arrays. It supports six data types: string, number, boolean, null, object, and array. JSON is the standard format for data exchange between web servers and browsers. Use our free JSON Formatter to beautify and validate JSON in your browser.
Introduction
JSON (JavaScript Object Notation) 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 — it is used by Python, Java, Go, Ruby, and virtually every modern programming language, not just JavaScript. JSON is defined by RFC 8259 and is the dominant data format for web APIs, configuration files, and NoSQL databases.
Step by Step
-
Understand JSON syntax
JSON uses curly braces {} for objects (key-value pairs), square brackets [] for arrays (ordered lists), and colons to separate keys from values. Keys must be strings in double quotes. Values can be strings, numbers, booleans, null, objects, or arrays.
-
Learn the six data types
JSON supports exactly six data types: string (in double quotes), number (no distinction between int/float), boolean (true or false), null, object ({...}), and array ([...]). JSON does not support undefined, functions, dates, or NaN.
-
Recognize JSON structure
A JSON document is either an object or an array at the top level. Objects contain key-value pairs; arrays contain ordered values. Structures can be nested to any depth — an object value can be another object or array.
-
Parse and generate JSON
In JavaScript, JSON.parse(string) converts a JSON string to a JavaScript object, and JSON.stringify(object) converts a JavaScript object to a JSON string. Every modern language has equivalent functions.
Examples
A simple JSON object
Input: Person with name and age
Output: {"name": "Alice", "age": 30}
JSON with nested structure
Input: User with address
Output: {"name": "Alice", "address": {"city": "NYC", "zip": "10001"}}
JSON array
Input: List of numbers
Output: [1, 2, 3, 4, 5]
Common Problems
- Using single quotes —JSON requires double quotes for all strings and keys. Single quotes are invalid.
- Trailing commas —a comma after the last item in an object or array is a syntax error in JSON.
- Comments —standard JSON does not support comments. Use JSONC or JSON5 if you need comments.
- Unquoted keys —unlike JavaScript object literals, JSON requires all keys to be in double quotes.
Tips
- JSON is language-independent despite its name —every modern language has JSON support.
- Use JSON for API requests and responses —it is the de facto standard, replacing XML.
- Validate JSON before sending it in an API request to avoid 400 errors.
- Use our JSON Formatter to beautify, validate, and minify JSON instantly in your browser.