JSON

in English: JavaScript Object Notation

basicwidespread

JSON is a simple, text-based data format in which programs exchange data in an organized, labeled form that is also human-readable.

In plain terms

Imagine you are filling out a form: on the left is the field name (Name, Year of birth, Address), on the right is what you enter. JSON is built on the same kind of label–value pairs. The difference is that it is not on paper but plain text, and it is meant not for a clerk but for another program. It can also contain lists and nested data structures.

It is useful for enabling two completely independent systems to understand each other. When your phone's weather app requests tomorrow's forecast, the server does not send back a ready-made screen but a JSON text, such as "city": "Szeged", "temperature": 14. The app draws what you see from this data.

How is it different from a Word document or an Excel spreadsheet? It contains no formatting, font, or color, only the data and its structure. This makes it relatively compact and easily handled by almost any programming language.

In the AI world, you hear about it often because agents typically communicate with other programs this way. When an AI agent creates a calendar entry or retrieves data, it usually formulates the request and the response in JSON, so the other program knows exactly what to do.

How it works

Data consists of key–value pairs: the key is the label in quotes, followed by a colon, then the value, for example "name": "Anna Kovács".
The value can be one of six types: text, number, true/false, null (empty value), list, or a new nested object.
Curly braces { } enclose a cohesive data package (an object), while square brackets [ ] enclose a list, such as the items in an order.
Since objects and lists can be nested, complex structures can be described: a customer, their multiple orders, and the items within those orders.
The receiving program reads and interprets the text; if even a single comma or quotation mark is missing, it considers the whole thing invalid and rejects it.

An everyday example

You order a pizza from your phone and see on the screen that the courier will arrive in seven minutes. In the background, the application regularly receives fresh data from the server, typically a short JSON text. This includes the order status, the courier's location, and the estimated arrival time. An AI agent typically uses the same format when booking a table or searching for a schedule on your behalf.

Who is affected

developerDaily work tool: services exchange data in this format, many configuration files are created in this format, and this is how tools usable by agents are described. → Code

employeeIf you export data from a system or automate a workflow, you will likely encounter a JSON file, which it is worth knowing how to read. → Work & HR

entrepreneur, executiveWhen connecting two corporate systems or allowing an AI agent access to your data, the question is often whether the system can send and receive data in JSON.

everyoneAlmost every application and website uses this in the background, and you often receive such a file when downloading your own data.

A common misconception

MythJSON is a programming language, and only those who can program in JavaScript understand it.

In realityJSON is not a language but a data description format: you cannot give commands or calculate in it, only record data. Its name originates from JavaScript, but today practically every programming language handles it, and with some practice, anyone can read it.

Limits and risks

The format is very strict: a single missing comma or quotation mark can render the entire file unusable.
Standard JSON does not allow comments. It also lacks a specific date type, so dates are stored as text. This often follows the ISO 8601 standard (for example, "2026-11-10"), but the format is determined by the agreement of the parties.
The format only guarantees that the data is written correctly, not that it is true: a language model can provide false or fabricated values even in perfectly formed JSON.
It contains no encryption or protection; passwords or personal data in the JSON file are readable just like plain text.

Similar, but not the same

XML – It is also used for data exchange, but works with opening and closing tags, making it more verbose; it is also used to describe documents. For simple data, JSON is shorter and easier to read.
CSV – CSV describes simple, table-like rows and columns, while JSON can handle nested, multi-level data structures.
JavaScript – JavaScript is the programming language with which you write working programs. JSON is only a way of writing data, linked to JavaScript by its name and notation.

Related concepts

Broader

Data format, Structured data, Adatcsere

Narrower

JSON schema, JSON Lines

On the edge

API, XML, YAML, Tool calling, Structured output, MCP

A brief history

The format was written and popularized by Douglas Crockford in the early 2000s, building on the JavaScript language for data notation. Its first internet description appeared in 2006 (RFC 4627). In 2013, it became a standard under the name ECMA-404, and the current version was fixed in 2017 by RFC 8259.

Where things stand

As of late 2026, JSON is the most widespread format for web and mobile data exchange, supported by almost every programming language and service. With the spread of AI agents it has become even more important, as tool calls and the structured outputs of language models typically rely on it.

Status: 2026 November

In the news

Appears in 1 Agent Age stories; the curve shows weekly occurrence in the news magazine.

Malicious files in the Downloads folder can hijack AI coding agents, researchers sayOct 26, 2026 · Code

Also known as

JSON · JavaScript Object Notation · json · .json · JSON file · JSON format · JSON format · JSON

Sources

This entry was machine-edited and has undergone machine expert review; the “In the news” section updates automatically from Agent Age stories.