JSON: Complete Guide to the Universal Data Format

What Is JSON?

JSON (JavaScript Object Notation) is a lightweight data-interchange format. Despite its name mentioning JavaScript, JSON is language-independent and is used across Python, Java, PHP, Go, Ruby, and virtually every modern programming language.

JSON has become the universal format for API communication, configuration files, and data storage because it is simple, human-readable, and easy for machines to parse.

JSON Syntax: Five Rules

Data is in key-value pairs: "name": "value"

Data is separated by commas

Curly braces hold objects: { }

Square brackets hold arrays: [ ]

Keys must be double-quoted strings

JSON Data Types

String: "Hello World" — must be double-quoted

Number: 42 or 3.14 — no quotes

Boolean: true or false — lowercase, no quotes

Null: null — lowercase, no quotes

Object: {"key": "value"} — curly braces with key-value pairs

Array: [1, 2, 3] or ["a", "b", "c"] — square brackets

A Complete JSON Example

{

"user": {

"id": 12345,

"name": "Ravi Kumar",

"email": "ravi@example.com",

"isActive": true,

"score": 98.5,

"address": null,

"skills": ["Python", "React", "SQL"],

"preferences": {

"theme": "dark",

"notifications": true

}

}

}

Parsing JSON in Different Languages

JavaScript: const data = JSON.parse(jsonString)

Python: import json; data = json.loads(json_string)

Java: Requires Gson or Jackson library

PHP: $data = json_decode($json_string)

Common JSON Mistakes

Single quotes instead of double quotes: {'name': 'value'} is invalid. Must be {"name": "value"}.

Trailing commas: {"a": 1, "b": 2,} is invalid. No comma after the last item.

Comments: JSON does not support comments. // and /* */ cause parse errors.

Undefined values: undefined is not a JSON type. Use null instead.

JSON vs JSON5 vs JSONC

JSON5 and JSONC (JSON with Comments) are supersets of JSON that add comments, trailing commas, and other conveniences. Used in some config files (VS Code settings.json uses JSONC). Not valid JSON — cannot be parsed by standard JSON.parse().