JSON and XML solve the same basic problem (representing structured data so different systems can exchange information), but with very different philosophies. Today JSON dominates most new use cases, but XML is still widely used, especially in older systems or specific contexts where its features make more sense.
Comparing the syntax
The same data represented in both formats:
JSON:
{
"person": {
"name": "Ana",
"age": 30
}
}XML:
<person>
<name>Ana</name>
<age>30</age>
</person>The most obvious difference is size: XML has to repeat each element’s name in both the opening and closing tags (<name> and </name>), while JSON just uses keys and values, with no repetition. This makes JSON consistently more compact for the same content.
Important structural differences
Attributes
XML has the concept of attributes, metadata that lives inside the opening tag itself.
// xml
<person id="123" active="true">
<name>Ana</name>
</person>JSON doesn’t have this concept. If you need to represent the same information, it just becomes another key inside the object.
// json
{
"id": "123",
"active": true,
"name": "Ana"
}This means that when converting XML to JSON, you need to decide on a convention for handling attributes (usually prefixing the key with @ or similar, depending on the conversion tool used).
Data types
JSON has native types: strings, numbers, booleans, null, objects, and arrays. XML doesn’t, everything is text by default.
<age>30</age>That 30 is a string from pure XML’s point of view. It’s up to the application consuming the XML to decide to convert it to a number, which requires an extra validation/schema layer (like XML Schema Definition, XSD) if you want to guarantee typing.
Comments
XML supports comments natively.
<!-- This is a comment -->
<person>
<name>Ana</name>
</person>JSON doesn’t support comments, as covered in other posts on the blog.
Namespaces
XML has a namespace system, useful for avoiding name conflicts when documents combine elements from different specifications/vocabularies. JSON has no direct equivalent; the convention is usually to use prefixes in the keys when needed, but that’s not part of the spec, it’s just a convention set by whoever designs the structure.
When XML still makes sense
- Documents with mixed structure (markup + data): XML was originally designed to represent documents (HTML itself derives from SGML), so it’s more natural for content where text and markup mix, like document formats (DOCX, ODT use XML internally)
- Legacy systems: many older enterprise integrations (SOAP, EDI) use XML, and migrating away from it is costly
- When you need strict schema validation: XSD is more mature and detailed than JSON’s equivalents (like JSON Schema), although the latter has been evolving quite a bit
- Digital signatures and encryption of specific parts of a document: XML has established standards for this (XML Signature, XML Encryption) more mature than JSON’s equivalents
When JSON is the better choice (most cases today)
- REST APIs: the de facto standard for client-server communication on the modern web
- Application configuration: more readable and easier to edit by hand
- When the main consumer is JavaScript: JSON maps directly to JavaScript objects, with no extra conversion
- When payload size matters: JSON is more compact, which matters on mobile connections or high-volume APIs
Quick summary
| JSON | XML | |
|---|---|---|
| Size | More compact | More verbose |
| Native types | Yes (string, number, boolean, null) | No (everything is text) |
| Attributes | No such concept | Yes |
| Comments | Not supported | Supported |
| Best for | Modern APIs, configuration | Documents, legacy systems, strict schemas |
In practice, if you’re starting a new project today and don’t have a specific reason to use XML (integrating with a legacy system, for example), JSON tends to be the simpler choice, and the one better supported by today’s tooling ecosystem.
If you need to convert data between the two formats, or just want to validate a JSON before using it, JSON Validator helps confirm the syntax is correct.