What Is JSON? A Simple Explanation with Examples

JSON (JavaScript Object Notation) is a lightweight text format for storing and exchanging data. When an app asks a server for your profile, the server almost certainly answers in JSON. It looks like this:

{
  "name": "VoltKit",
  "launched": 2026,
  "free": true,
  "categories": ["tools", "games", "learn"]
}

That is a complete JSON document: an object with four keys, whose values are a string, a number, a boolean and an array. It is readable by people and trivially parsed by machines, which is why it has become the default way software talks to software.

The six value types

JSON has only six kinds of value, and every document is built from them:

Type	Example	Notes
String	"hello"	Always double quotes; backslash escapes such as \n
Number	42, -3.5, 1e9	No leading zeros, no NaN or Infinity
Boolean	true, false	Lowercase only
Null	null	Represents "no value"
Array	[1, 2, 3]	Ordered list of any values
Object	{"key": "value"}	Unordered set of key–value pairs; keys are strings

Objects and arrays can nest without limit, so a JSON document can describe anything from a single number to a whole database export.

How JSON is used

• Web APIs. Nearly every REST API sends and receives JSON. The Content-Type: application/json header tells the receiver how to read the body.
• Configuration. package.json, tsconfig.json, editor settings and countless other config files are JSON.
• Storage. Browsers store JSON strings in localStorage; document databases such as MongoDB and CouchDB store JSON-like records natively.
• Data exchange. Exports, logs and messages between services are commonly JSON because every language has a parser built in.

In JavaScript, converting between text and objects is one call each way:

const text = JSON.stringify({ ok: true }); // '{"ok":true}'
const value = JSON.parse(text);            // { ok: true }

JSON vs XML

Before JSON, XML was the usual exchange format. XML is more verbose (<name>VoltKit</name> versus "name": "VoltKit"), supports attributes, namespaces and schemas, and is still common in enterprise and document systems such as SOAP, RSS and Office files. JSON won the web because it is smaller, maps directly onto the data structures programmers already use, and needs no extra library in the browser.

Common JSON mistakes

Most invalid JSON is JavaScript that is not quite JSON. Watch for:

• Trailing commas after the last item: {"a": 1,} is invalid.
• Single quotes or unquoted keys: {'a': 1} and {a: 1} are invalid.
• Comments, which JSON does not allow.
• undefined, NaN and Infinity, which have no JSON representation. Use null or a string.
• Leading zeros such as 007, which must be written as 7 or quoted.

A validator catches all of these and points to the exact line and column:

Check your JSON withJSON Validator

Related concepts

• YAML is a superset of JSON used for configuration; it trades braces for indentation. The JSON to YAML converter shows the same data in both.
• CSV is flat and tabular; JSON is nested. The JSON to CSV converter flattens nested keys into columns.
• JSON Schema describes what a JSON document should contain, so it can be validated automatically.
• JWT tokens are three Base64-encoded JSON objects joined with dots; the JWT decoder shows them.