JSON vs XML: Which Data Format Should You Use in 2025?

Meta Description: JSON vs XML compared — performance, readability, features, and use cases. Learn which data format is right for your APIs, config files, and data exchange needs.

The JSON vs XML debate has been going on for nearly two decades, and at this point, it's not really a debate anymore. JSON won the API wars. But XML isn't dead — it's deeply entrenched in enterprise systems, document formats, and specific domains where its features genuinely matter.

The right answer isn't "always JSON" or "always XML." It's understanding what each format does well and picking the tool that fits.

The Quick Version

If you're building a REST API: use JSON. If you're working with SOAP, XSLT, or enterprise integrations: XML is probably required. If you're starting a new project with no legacy constraints: JSON, almost certainly.

Now let's dig into why.

JSON: The Modern Default

JSON (JavaScript Object Notation) emerged from the JavaScript world and became the dominant data interchange format for web APIs around 2010. Its appeal is simplicity.

{
  "employee": {
    "name": "Alice Chen",
    "department": "Engineering",
    "skills": ["Python", "Go", "SQL"],
    "active": true,
    "salary": 95000
  }
}

What JSON does well:

• Lightweight. Minimal syntax overhead. No closing tags, no attributes vs. elements confusion.
• Native in JavaScript. JSON.parse() and JSON.stringify() are built-in. No library needed.
• Fast to parse. Simpler grammar means parsers are faster. Benchmarks consistently show JSON parsing at 2-10x faster than XML.
• Easy to read. Most developers can scan a JSON document and understand it immediately.
• Data types. Strings, numbers, booleans, null, arrays, objects — the six types cover most use cases.

What JSON lacks:

• No comments. This hurts for config files.
• No schema built-in. JSON Schema exists but isn't part of the format itself.
• No namespaces. When combining data from multiple sources, naming conflicts are your problem.
• No processing instructions. No way to include metadata about how to process the document.
• Limited number precision. JSON numbers follow IEEE 754, which means large integers (>2^53) lose precision in JavaScript.

XML: The Enterprise Standard

XML (eXtensible Markup Language) was standardized in 1998. It's verbose, feature-rich, and powers an enormous amount of infrastructure.

<?xml version="1.0" encoding="UTF-8"?>
<employee>
  <name>Alice Chen</name>
  <department>Engineering</department>
  <skills>
    <skill>Python</skill>
    <skill>Go</skill>
    <skill>SQL</skill>
  </skills>
  <active>true</active>
  <salary currency="USD">95000</salary>
</employee>

What XML does well:

• Self-describing with schemas. XSD (XML Schema Definition) provides rigorous type validation, data constraints, and documentation.
• Namespaces. Multiple vocabularies can coexist in one document without conflicts.
• Attributes. Metadata can live on elements via attributes, keeping data and metadata separate.
• XSLT transformations. A full transformation language for converting XML between formats.
• XPath queries. Powerful query language for navigating XML documents.
• Comments. <!-- This is a comment --> — simple, useful, supported.
• Mixed content. Text and markup can be interleaved, essential for document formats.
• Mature tooling. Decades of enterprise tools, validators, and libraries.

What XML struggles with:

• Verbosity. Closing tags double the markup overhead. The same data is often 30-50% larger in XML.
• Complexity. Namespaces, schemas, DTDs, CDATA sections — the learning curve is steep.
• Parsing speed. More complex grammar means slower parsers.
• No native data types. Everything in XML is text. <age>30</age> — is that a number? A string? XML doesn't know without a schema.
• Browser support. JavaScript's XML APIs (DOMParser, XHR) are clunkier than JSON.parse().

Head-to-Head Comparison

When JSON Wins

REST APIs

This is JSON's home turf. The combination of lightweight syntax, native browser support, and fast parsing makes it the obvious choice for web APIs.

// API Response
{
  "status": "success",
  "data": {
    "users": [
      {"id": 1, "name": "Alice"},
      {"id": 2, "name": "Bob"}
    ]
  },
  "meta": {
    "total": 2,
    "page": 1
  }
}

The same data in XML would be roughly twice the size and require more code to parse on the client.

Mobile Applications

Bandwidth matters on mobile. JSON's smaller payload size means faster transfers and less data usage. Most mobile networking libraries (Retrofit, Alamofire, Axios) handle JSON natively.

Microservices Communication

Services talking to services need speed and simplicity. JSON over HTTP (or gRPC with Protobuf for maximum performance) is the standard pattern. XML's overhead doesn't buy anything in service-to-service communication.

Configuration Files

With the caveat that JSON doesn't support comments (use JSON5 or JSONC instead), JSON config files are common:

{
  "database": {
    "host": "localhost",
    "port": 5432,
    "name": "myapp"
  },
  "cache": {
    "ttl": 3600,
    "maxSize": "256mb"
  }
}

NoSQL Databases

MongoDB, CouchDB, and DynamoDB store data as JSON (or BSON, a binary JSON variant). If your database speaks JSON, your API should too.

When XML Wins

Document Formats

HTML is technically XML-adjacent (XHTML was strict XML). Office documents (DOCX, XLSX) are zipped XML. SVG graphics are XML. ePub books are XML.

XML's mixed-content model — where text and markup interleave — is essential for documents:

<paragraph>
  This is <bold>important</bold> text with
  <link href="/page">a link</link> in it.
</paragraph>

JSON can't represent this naturally.

Enterprise Integration

SOAP web services, EDI (Electronic Data Interchange), banking protocols (ISO 20022), and healthcare standards (HL7 FHIR supports both, but XML is traditional) are XML-based. If you're integrating with enterprise systems, you'll speak XML.

Complex Validation

When you need to enforce complex data rules — element ordering, occurrence constraints, type hierarchies, cross-field validation — XSD is more powerful than JSON Schema:

<xs:element name="age" type="xs:integer" minInclusive="0" maxInclusive="150"/>
<xs:element name="email" type="xs:string">
  <xs:pattern value="[^@]+@[^@]+\.[^@]+"/>
</xs:element>

Transformations

XSLT can transform XML from one structure to another declaratively. Need to convert an invoice XML to an HTML report? XSLT does it without imperative code:

<xsl:template match="invoice">
  <html>
    <h1>Invoice #<xsl:value-of select="@number"/></h1>
    <xsl:apply-templates select="items/item"/>
  </html>
</xsl:template>

JSON has no equivalent standard. You'd write transformation code in your programming language.

Digital Signatures and Encryption

XML Signature and XML Encryption are W3C standards for signing and encrypting parts of an XML document. This is important in security-sensitive contexts like SAML authentication and signed legal documents.

Migration: XML to JSON

Many organizations are migrating from XML to JSON for their APIs. Key considerations:

Data loss risks:

• XML attributes have no direct JSON equivalent (flatten them or use conventions)
• XML ordering is significant; JSON object key order is not guaranteed
• XML namespaces require a naming convention in JSON
• Mixed content (text + elements) is hard to represent in JSON

Practical approach:

1. Add JSON support alongside XML (don't break existing clients)
2. Default new endpoints to JSON
3. Deprecate XML endpoints with a timeline
4. Provide conversion documentation

Performance Benchmarks

Real-world numbers vary by language and library, but typical patterns:

After gzip compression, the size difference narrows significantly because XML's repetitive tags compress well. But the parsing speed advantage persists.

Tools for Working with Both

Need to format, validate, or convert JSON? Our JSON formatter handles formatting, validation, and minification instantly. Paste your JSON and get clean, readable output with syntax highlighting and error detection.

For converting between JSON and XML, tools like xml2json or online converters can help during migration projects.

The Verdict

For new projects: JSON. Unless you have specific requirements that demand XML (document markup, enterprise integration, complex schemas), JSON is the right default. It's simpler, faster, smaller, and supported everywhere.

For existing XML systems: Don't rewrite just because JSON is trendy. If your XML infrastructure works, keep it. Add JSON endpoints for new consumers if needed.

For documents: XML. It was designed for this, and nothing else does it better.

For config files: JSON5/JSONC or YAML (if you need comments), JSON (if you don't).

The format wars are over. Both formats survived because they're good at different things. Pick the one that fits your use case.

FAQ

Can I convert JSON to XML and back without losing data?

Not always. XML has features (attributes, namespaces, comments, processing instructions, mixed content) that don't have direct JSON equivalents. Simple data structures convert cleanly, but complex XML documents may lose nuance in translation.

Why did JSON replace XML for most APIs?

Three reasons: smaller payload size (30-50% less markup), faster parsing in browsers, and native JavaScript support. As the web shifted to JavaScript-heavy frontends, JSON became the natural choice for client-server communication.

Is GraphQL replacing JSON APIs?

GraphQL uses JSON as its response format. It replaces REST's URL-based resource model with a query language, but the data still travels as JSON. They're complementary, not competing.

Should I use JSON or YAML for configuration?

YAML supports comments and is more human-friendly for complex configs. JSON is simpler and has stricter parsing (fewer surprises). For Kubernetes, Docker Compose, and CI/CD: YAML is standard. For application configs: either works, but YAML's comment support is a significant advantage.

Is XML dying?

No. XML is declining in new API development but remains deeply embedded in enterprise systems, document formats (DOCX, SVG, ePub), and industry standards (healthcare, finance, government). It'll be around for decades.