What does JSON stand for? It stands for JavaScript Object Notation, a lightweight text format for writing down structured data so that programs can store it or pass it to each other. A JSON file is just readable text made of names, values, lists and curly braces.
Although the name mentions JavaScript, the format is not tied to one language. Nearly every modern programming language can read and write it, which is why it became the everyday way for apps, websites and servers to swap information. When your weather app asks a server for today's forecast, the answer very often comes back as JSON.
Quick facts
Stands for
JavaScript Object NotationType
Acronym, said "JAY-sun"What it is
A text format for structured dataFile extension
.jsonUsed for
Web APIs, config files, saved settings, data exchangeNot to be confused with
JavaScript itself, which is a programming language
What does JSON stand for? The full form, word by word
- JavaScript: the syntax was borrowed from the way the JavaScript language writes objects.
- Object: the main building block, a set of name and value pairs wrapped in curly braces.
- Notation: a way of writing something down. JSON is a notation, not a program.
The format was popularized in the early 2000s by programmer Douglas Crockford, who described it as a simpler choice for sending data than the heavier formats common at the time. It has since been written up as a formal standard, so a JSON file made in one language reads the same in any other.
What JSON looks like
Here is a small JSON record for a library book:
{ "title": "River Days", "pages": 212, "available": true, "tags": ["history", "travel"], "borrower": null }
Read it as: the title is the text River Days, the page count is the number 212, the book is available, it has two tags in a list, and nobody has borrowed it.
JSON allows only a handful of value types:
| Type | Looks like | Notes |
|---|---|---|
| String | "hello" | Always in double quotes |
| Number | 42 or 3.14 | No quotes, no leading zeros |
| Boolean | true or false | Lowercase only |
| Null | null | Means no value |
| Array | [1, 2, 3] | An ordered list in square brackets |
| Object | {"a": 1} | Name and value pairs in curly braces |
Rules that trip people up
- Double quotes only. Names and text strings need "double" quotes. Single quotes make the file invalid.
- No trailing commas. A comma after the last item in a list or object breaks the file.
- No comments. Standard JSON has no way to write notes inside the file.
- Names must be strings. Every key is quoted, even simple ones.
- No dates as a type. Dates are usually stored as text in a set format.
A tool called a JSON validator or linter will point to the exact line where one of these rules is broken, which saves a lot of squinting.
Where you will run into JSON
Most people meet JSON without knowing it. Some common places:
- Web APIs: when one program asks another for data over HTTP, the reply is often JSON. An API doc will show sample JSON responses.
- Settings files: code editors, games and apps often save preferences in a .json file.
- Data exports: some services let you download your account data as JSON.
- Databases: some databases store whole JSON documents, and others offer JSON columns next to regular tables.
More of the letters you see in coding live on the tech acronyms hub.
JSON vs similar formats
- JSON vs CSV: CSV is a flat table of rows and columns. JSON can nest lists inside objects inside lists, so it handles more complex records.
- JSON vs XML: XML uses opening and closing tags and is wordier. JSON is shorter and usually easier to read.
- JSON vs HTML: HTML describes how a web page is laid out. JSON just holds data with no layout at all.
- JSON vs JavaScript: JavaScript is a full programming language. JSON is only a data format, and valid JSON is stricter than JavaScript object code.
Saying and writing it
Most developers say JSON like the name Jason, "JAY-sun." A smaller group says "jay-SAWN." Both are heard at work. The opening j sound means it takes a: "a JSON file," "a JSON response." Write it in capitals in prose, and use lowercase only for the file extension, .json.
The official media type that servers send with this data is application/json, which you may see in a browser's developer tools.
Questions people ask
Is JSON a programming language?
No. It is a data format, a set of rules for writing data as text. Programs written in many languages read and write it, but JSON itself cannot run or make decisions.
Do you need JavaScript to use JSON?
No. The name comes from JavaScript's object syntax, but almost every modern language, from Python to PHP, has built in or standard tools for JSON.
How do I open a JSON file?
Any plain text editor will open it, because it is just text. Code editors and many browsers can also show it with colors and folding so it is easier to read.
Can JSON have comments?
Standard JSON does not allow comments. Some tools accept a relaxed version with comments, but a strict parser will reject them.
What is the JSON full form?
The full form is JavaScript Object Notation. In speech and writing, almost everyone just uses the short form.