JSON vs XML: Which Should You Use in 2025?

The Great Data Format Debate

If you've been in tech for more than five minutes, you've probably witnessed (or participated in) the JSON vs XML debate. It's like tabs vs spaces, but for data formats.

Here's the truth: both are good at different things. The "which is better" question is like asking "which is better: a hammer or a screwdriver?" Depends on what you're building.

Let's break down this rivalry with actual facts instead of tribal warfare.

Same Data, Different Syntax

Before we dive into the differences, let's see how the same data looks in both formats. We'll use a simple user profile:

In JSON

{
  "user": {
    "id": 1,
    "name": "Alice Johnson",
    "email": "alice@example.com",
    "roles": ["admin", "editor"],
    "active": true,
    "metadata": {
      "createdAt": "2024-01-15",
      "lastLogin": "2024-11-27"
    }
  }
}

In XML

<?xml version="1.0" encoding="UTF-8"?>
<user>
  <id>1</id>
  <name>Alice Johnson</name>
  <email>alice@example.com</email>
  <roles>
    <role>admin</role>
    <role>editor</role>
  </roles>
  <active>true</active>
  <metadata>
    <createdAt>2024-01-15</createdAt>
    <lastLogin>2024-11-27</lastLogin>
  </metadata>
</user>

Notice anything? The JSON version is ~40% smaller. That's because XML requires opening AND closing tags for every element. JSON just needs a colon and the value.

JSON Advantages

1. Smaller File Size

Less verbose = smaller files = faster transmission = happier users. On mobile networks or when serving millions of requests, this adds up fast.

Same data comparison:
├── JSON: 247 bytes
├── XML:  412 bytes
└── Difference: 40% larger for XML

2. Native JavaScript Parsing

This is JSON's superpower. JavaScript can parse JSON with a single built-in function:

// JSON - Built-in, one line
const data = JSON.parse(jsonString);

// XML - Requires parsing, more code
const parser = new DOMParser();
const xmlDoc = parser.parseFromString(xmlString, "text/xml");
const name = xmlDoc.querySelector("name").textContent;

With JSON, you get a ready-to-use JavaScript object. With XML, you get a document you need to traverse and extract data from.

3. Better for APIs

REST APIs overwhelmingly use JSON. Here's a real-world API response example:

// Modern API call with JSON
const response = await fetch('/api/users');
const users = await response.json();  // Direct to JS object

// Work with data immediately
users.forEach(user => {
  console.log(user.name);
});

4. Human Readable

Both formats are human-readable, but JSON is more readable. Less noise, more signal:

{"name": "Clean", "score": 100}

vs.

<data><name>Clean</name><score>100</score></data>

XML Advantages

Don't count XML out just yet. It has legitimate advantages:

1. Comments Support

XML supports comments. JSON doesn't. For configuration files that humans edit, this is a big deal:

<?xml version="1.0"?>
<config>
  <!-- Database configuration -->
  <database>
    <host>localhost</host>
    <!-- Use 5432 for PostgreSQL, 3306 for MySQL -->
    <port>5432</port>
  </database>
</config>

2. Namespaces

When combining documents from different sources, XML namespaces prevent conflicts:

<root xmlns:book="http://example.com/book"
      xmlns:author="http://example.com/author">
  <book:title>The Great Gatsby</book:title>
  <author:name>F. Scott Fitzgerald</author:name>
</root>

3. Built-in Validation (DTD/XSD)

XML has mature schema validation built into the standard:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="user">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="name" type="xs:string"/>
        <xs:element name="age" type="xs:integer"/>
        <xs:element name="email" type="xs:string"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

JSON Schema exists too, but it's not part of the JSON spec itself.

4. XSLT Transformations

XML can be transformed using XSLT — a powerful way to convert XML to other formats (HTML, PDF, other XML structures) using templates.

5. Better for Document Markup

HTML, SVG, and RSS are all XML-based. When you need mixed content (text with embedded tags), XML excels:

<paragraph>
  This is <bold>important</bold> text with 
  <link href="http://example.com">a link</link> inside.
</paragraph>

JSON can't do this elegantly.

Performance Comparison

Let's talk numbers. Here's what the benchmarks show:

* Benchmarks are approximate and vary by implementation and data complexity

When to Use What

Choose JSON When:

• Building REST APIs or web services
• Working with JavaScript/Node.js applications
• Storing data in NoSQL databases (MongoDB, CouchDB)
• Creating configuration files for modern tools
• Building mobile apps that need efficient data transfer
• Doing real-time communication (WebSockets, Server-Sent Events)

Choose XML When:

• Working with enterprise SOAP services
• You need document validation with complex schemas
• Dealing with legacy systems that expect XML
• Building document markup (like XHTML, RSS, Atom)
• You need namespaces to combine multiple vocabularies
• Using XSLT for document transformations

Migration Tips: XML to JSON

Moving from XML to JSON? Here are the gotchas:

Attributes vs Properties

<user id="1" active="true">
  <name>Alice</name>
</user>

Becomes:

{
  "user": {
    "id": 1,
    "active": true,
    "name": "Alice"
  }
}

Repeated Elements to Arrays

<users>
  <user>Alice</user>
  <user>Bob</user>
</users>

Becomes:

{
  "users": ["Alice", "Bob"]
}

Mixed Content — The Hard Part

If your XML has mixed content (text with inline tags), you'll need to restructure the data or use a special format convention.

The Verdict

In 2025, here's the reality:

• JSON dominates for web development and APIs
• XML persists in enterprise, documents, and legacy systems
• New projects almost always choose JSON
• Both are valid — context determines the right choice

The "war" is basically over. JSON won the web, but XML isn't going anywhere. Know both, use the right tool for the job, and don't get religious about it.

Frequently Asked Questions

Is JSON faster than XML?

Yes, in most scenarios. JSON parsing in JavaScript is 2-3x faster than XML parsing, and JSON files are typically 30-50% smaller.

Can I convert XML to JSON automatically?

Yes, but not perfectly. XML attributes, namespaces, and mixed content don't have direct JSON equivalents. You'll need to make decisions about how to represent them.

Why do some APIs still use XML?

Usually legacy reasons. Many enterprise systems were built on SOAP/XML and changing them would be expensive and risky. "If it ain't broke..."

Is XML dying?

No, but it's mature and not growing. New projects rarely choose XML for data exchange, but it remains essential for document formats (SVG, XHTML, Office documents).

Related Reading

• What is JSON? — Complete beginner's guide
• JSON to YAML — Another format comparison
• JSON Schema — Validate JSON like XML's XSD