JSON is the default for REST APIs, mobile clients, and NoSQL storage — smaller payloads and native parsing make it the practical choice whenever you control both ends of the wire. In a head-to-head test of the same record (see the examples below), the minified XML version came out about 39% larger than the equivalent JSON, purely from closing tags. XML remains the right call for SOAP-based enterprise APIs, RSS/Atom feeds, and any format needing attributes, namespaces, or mixed text-and-markup content — banking, healthcare, and government systems built on decades of XML infrastructure aren't migrating off it for a payload-size win alone.
JSON
JSON (JavaScript Object Notation) is a lightweight, text-based data-interchange format defined by RFC 8259. It represents data as nested objects and arrays using just six structural characters — no closing tags, and no schema is required for a document to be valid.
Pros
- • Less verbose than XML — no closing tags to repeat
- • Parses natively into JavaScript objects with zero translation layer
- • Rich native data types: string, number, boolean, null, array, object
- • Smaller payload size — roughly 30-40% smaller than the equivalent XML for a typical record
- • The default for REST APIs, NoSQL document stores, and most modern language standard libraries
- • Simple enough to hand-write or hand-edit without needing a schema
Cons
- • No native support for attributes — everything must be expressed as a key/value pair
- • No namespace support, so merging data from multiple sources risks key collisions
- • Comments are not part of the grammar (RFC 8259)
- • Native schema tooling is weaker than XML — JSON Schema is optional and less mature than XSD
Example
{
"book": {
"id": 101,
"title": "Clean Code",
"author": "Robert C. Martin",
"tags": ["software", "engineering"]
}
} XML
XML (eXtensible Markup Language) is a markup-based format standardized by the W3C. It represents data as a tree of tagged elements that can carry attributes and belong to namespaces, making it equally suited to documents and structured data.
Pros
- • Mature, strict schema validation via XSD and DTD
- • Native support for attributes as element metadata
- • Namespaces prevent tag-name collisions when merging documents from different sources
- • Handles mixed content — text interleaved with markup — far better than JSON
- • Backbone of long-established standards: SOAP APIs, RSS/Atom feeds, SVG, DocBook
- • Comments are part of the spec
Cons
- • Significantly more verbose — closing tags and angle brackets add real overhead
- • Slower to parse — requires building a DOM or SAX parser rather than a native call
- • Every value is text by default; types must be inferred or declared via a schema
- • Awkward to hand-edit compared to JSON for simple key/value data
Example
<book id="101">
<title>Clean Code</title>
<author>Robert C. Martin</author>
<tags>
<tag>software</tag>
<tag>engineering</tag>
</tags>
</book> Want to convert between data formats?
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