JSON Syntax: A Complete Guide for Developers

JSON (JavaScript Object Notation) is the most widely used data format for APIs and configuration files. Understanding its syntax is essential for every developer.

What is JSON?

JSON is a lightweight, text-based data interchange format. Despite its name, JSON is language-independent and used across virtually every programming language.

Basic Structure

JSON is built on two structures:

Objects

Objects are collections of key-value pairs enclosed in curly braces:

{"name": "John", "age": 30}

Keys must be strings in double quotes. Values can be any valid JSON data type.

Arrays

Arrays are ordered lists of values enclosed in square brackets:

["apple", "banana", "cherry"]

Arrays can contain any combination of data types, including other arrays and objects.

Data Types

JSON supports six data types:

Strings

Strings must be enclosed in double quotes (not single quotes):

{"message": "Hello, World!"}

Special characters must be escaped with a backslash.

Numbers

Numbers can be integers or floating-point, positive or negative:

{"integer": 42, "float": 3.14, "negative": -10}

JSON doesn't support special values like NaN or Infinity.

Booleans

Boolean values are lowercase true or false:

{"isActive": true, "isDeleted": false}

Null

Null represents an empty or non-existent value:

{"middleName": null}

Objects

Objects can be nested within other objects:

{"person": {"name": "John", "age": 30}}

Arrays

Arrays can contain any data type:

{"numbers": [1, 2, 3], "mixed": [1, "two", true, null]}

Common Syntax Rules

Keys Must Be Strings

Keys must always be double-quoted strings:

Correct: {"name": "John"}

Wrong: {name: "John"}

No Trailing Commas

JSON doesn't allow trailing commas:

Correct: {"a": 1, "b": 2}

Wrong: {"a": 1, "b": 2,}

No Comments

JSON doesn't support comments. This is one of its limitations:

Wrong: {"name": "John" // this is a comment}

Double Quotes Only

Always use double quotes, never single quotes:

Correct: {"name": "John"}

Wrong: {'name': 'John'}

Escaping Special Characters

Use backslash to escape special characters in strings:

Example: {"message": "Line 1\nLine 2"}

Nested Structures

JSON excels at representing complex, nested data:

{

"company": "Acme Corp",

"employees": [

{"name": "John", "role": "Developer"},

{"name": "Jane", "role": "Designer"}

],

"address": {

"street": "123 Main St",

"city": "New York"

}

}

Whitespace

JSON ignores whitespace between elements. These are equivalent:

{"name":"John"}

{

"name": "John"

}

Use whitespace for readability in development, remove it for production to reduce file size.

Conclusion

JSON's simple syntax makes it easy to read and write. Use JSONSpark to format, validate, and minify your JSON data quickly.