What is JSON? A Beginner's Guide for Developers

What Does JSON Stand For?

JSON stands for JavaScript Object Notation. It 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 "JavaScript" being in the name, JSON is completely language-independent — it is used in Python, Java, PHP, Go, Ruby, Swift, and virtually every other programming language in active use today.

JSON was created by Douglas Crockford in the early 2000s as a simpler alternative to XML for transmitting data between a server and a web application. It became the dominant data format for web APIs and has since expanded into configuration files, databases, and data storage across all of software development.

JSON Syntax: The Basics

JSON is built on two structures: objects (collections of key-value pairs) and arrays (ordered lists of values). Here is a simple JSON object representing a user:

Every JSON document follows a handful of rules:

• Keys must be strings in double quotes — "name", not name or 'name'
• Strings must use double quotes — single quotes are not valid JSON
• Values can be strings, numbers, booleans, null, objects, or arrays
• No trailing commas — the last item in an object or array must not have a comma after it
• No comments — unlike JavaScript, JSON does not support // or /* */ comments

JSON Data Types

JSON supports exactly six data types:

• String — Text wrapped in double quotes: "hello world"
• Number — Integer or decimal: 42, 3.14, -7
• Boolean — Either true or false (lowercase, no quotes)
• Null — Represents an intentionally absent value: null
• Object — A collection of key-value pairs: {"key": "value"}
• Array — An ordered list of values: [1, "two", true, null]

Note what JSON does not support: dates (use ISO 8601 strings like "2026-06-01"), functions, undefined, and special number values like Infinity or NaN. These are JavaScript-specific features that are not part of the JSON specification.

What is JSON Used For?

Web APIs

The most common use of JSON is as the data format for REST APIs — the interfaces that allow web applications and services to communicate with each other. When you use a weather app, book a flight online, or log in with Google, your browser or app is almost certainly sending and receiving JSON data behind the scenes.

Configuration Files

Many developer tools use JSON for configuration: package.json for Node.js projects, tsconfig.json for TypeScript, .eslintrc.json for linting rules, and countless others. These files define project settings in a format that is both human-readable and easily parsed by build tools.

Data Storage and Databases

Document databases like MongoDB store data in BSON (Binary JSON), a binary-encoded form of JSON. Many relational databases including PostgreSQL and MySQL now support native JSON columns, allowing developers to store flexible structured data alongside traditional relational tables.

Data Exchange and Export

Applications export and import data in JSON format for portability. Analytics dashboards, CRM systems, e-commerce platforms, and many SaaS tools offer JSON export for integration with other systems or for data backup.

JSON vs XML: Why JSON Won

Before JSON became dominant, XML (Extensible Markup Language) was the standard format for data interchange. JSON displaced XML for most web use cases for several practical reasons: JSON is significantly more compact — representing the same data requires far fewer characters. JSON maps directly to native data structures in JavaScript and most other languages, making it trivial to parse. JSON is easier to read and write by hand. And JSON has no optional complexity — there are no attributes, namespaces, or schemas to contend with for basic use cases.

XML still has advantages in document-centric use cases where mixed content, namespaces, and extensive validation are needed — but for the vast majority of API and data exchange scenarios, JSON is the clear practical choice.

Common JSON Errors and How to Fix Them

• Trailing comma — A comma after the last item in an object or array is invalid JSON. This is allowed in JavaScript but not in JSON.
• Single quotes — All keys and string values must use double quotes. Single-quoted strings are not valid.
• Unquoted keys — Unlike JavaScript object literals, JSON requires all keys to be quoted strings.
• Comments — JSON does not support comments. If you need comments in a config file, consider JSONC (JSON with Comments), used by VS Code.
• Mismatched brackets — Every { must have a matching } and every [ must have a matching ]. Nesting errors are among the most common in large JSON files.

How to Validate and Format JSON

When working with JSON — whether debugging an API response, editing a config file, or reading data exports — a formatter and validator is indispensable. The WorldMerch JSON Formatter takes raw or minified JSON, validates its syntax, highlights any errors, and reformats it with clean indentation so it is easy to read.