JSON vs XML: which should you use?

The same data, two formats

Here's a small record in both formats. First XML:

<user>
  <id>1</id>
  <name>Ada</name>
  <roles>
    <role>admin</role>
    <role>editor</role>
  </roles>
</user>

And the same thing in JSON:

{
  "id": 1,
  "name": "Ada",
  "roles": ["admin", "editor"]
}

JSON expresses the list and the number directly; XML wraps everything in named tags and treats all content as text. That difference drives everything below.

How they compare

Verbosity and size

XML repeats each field name in an opening and closing tag, so it's noticeably larger than the equivalent JSON. For chatty APIs that adds up.

Data types

JSON has native numbers, booleans, null, arrays, and objects. In XML everything is text unless a separate schema (XSD) assigns types, so consumers must interpret values themselves.

Expressiveness

XML offers features JSON deliberately lacks: attributes, namespaces, comments, mixed content, and rich schema validation. For document markup and complex enterprise contracts, that power is useful.

Tooling and parsing

Browsers parse JSON natively and it maps straight onto language data structures. XML has mature tooling too (XPath, XSLT, XSD), but it's heavier to work with in a typical web app.

When to use each

• Use JSON for web and mobile APIs, configuration, and anywhere data maps cleanly to objects and arrays.
• Use XML for document-centric formats, systems that require namespaces or schema validation, and legacy or enterprise integrations that expect it.

Why JSON became the default

As the web shifted to JavaScript-heavy front ends, a format that the browser could parse natively and that matched JavaScript's own objects had an obvious edge. JSON was smaller, simpler, and required no extra libraries — so it steadily replaced XML for most public APIs. If you're working with JSON now, you can view and validate it, turn array data into a table, or explore large documents in the workspace.

Frequently asked questions

What is the main difference between JSON and XML?

JSON encodes data as key/value pairs, arrays, and primitives with a lightweight syntax. XML is a markup language that wraps data in named tags and supports attributes, namespaces, and schemas. JSON is more compact; XML is more expressive for documents.

Is JSON faster than XML?

Generally yes for typical web payloads: JSON is smaller and parses faster in browsers via the native JSON parser. XML parsing is heavier, though the gap depends on the data and tooling.

Why did JSON replace XML for most web APIs?

JSON maps directly to the data structures of modern languages, is less verbose, and is parsed natively in the browser. That made it the natural fit for JavaScript-driven web APIs.

Does JSON support comments and attributes like XML?

No. JSON has no comments and no attribute concept — everything is a value. XML supports comments, attributes, namespaces, and schema validation out of the box.