What Is JSON? The Web's Data Format Explained

What JSON is

JSON (JavaScript Object Notation) is a lightweight, text-based format for storing and exchanging data. It is how one program sends structured information to another in a way both humans and machines can read easily. When an app on your phone fetches your feed, or a website loads data without refreshing, the information is very often traveling as JSON. Despite the name, it is language-independent, virtually every programming language can read and write it, which is a big part of why it became ubiquitous.

Why it took over

JSON became the default data format of the modern web because it is simple, compact, and readable. It grew out of JavaScript's object syntax, so it slotted naturally into web development, but its plain-text simplicity made it easy to adopt everywhere. Compared to older formats, it has less clutter, which means smaller payloads and less parsing overhead. That combination of human-readability and machine-efficiency is why nearly every web API today speaks JSON by default.

The building blocks

JSON is built from a few simple pieces. Data is written as name/value pairs, like "name": "Ada". Values can be strings (text in quotes), numbers, booleans (true or false), null, and two container types: objects and arrays. An object, wrapped in curly braces, groups related pairs together. An array, wrapped in square brackets, is an ordered list of values. Because objects and arrays can nest inside each other, JSON can represent everything from a single value to deeply structured data with just these building blocks.

A quick example

A JSON snippet describing a person might group a name and age in an object, and include an array of hobbies: a name/value pair for the name, another for the age, and a list in brackets for the hobbies. Even without knowing the syntax rules in detail, you can usually read a JSON document and understand what it represents, which is exactly the point. That readability makes it easy to inspect API responses, debug data, and hand-write configuration.

JSON vs XML

Before JSON, XML was the dominant format for exchanging data. XML is powerful and still used in many systems, but it is more verbose, wrapping data in opening and closing tags that add bulk and make it harder to read at a glance. JSON conveys the same structure with far less text. XML still has strengths for certain document-heavy or highly formal uses, but for the typical job of sending structured data between web services, JSON's simplicity won out.

Where you'll encounter it

Even if you never write code, JSON is everywhere behind the scenes: web and mobile APIs, configuration files for developer tools, data exports, and settings all commonly use it. For anyone learning programming or working with APIs, understanding JSON is essential, it is the lingua franca of data on the web. The good news is that its whole design goal is simplicity, so once you recognize objects, arrays, and name/value pairs, you can read almost any JSON you come across.

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See also: What is an API? Explained for beginners, Frontend vs backend development explained.

Sources

• JSON - Wikipedia
• Introducing JSON (json.org)

Published date reflects the original event date (2025-07-01). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.