JSON vs XML: which should you use?
Compare readability, verbosity, tooling, schema support and performance between JSON and XML in modern systems.
By JSON Formatter Team
The short answer
For new REST or GraphQL APIs, use JSON. For document-centric formats with rich metadata (SOAP, SVG, XHTML, config files with schemas), XML is still a fine fit.
Verbosity
XML wraps every value in an open and close tag. JSON expresses the same data in roughly 30–40% less bytes on the wire, which matters at API scale.
Tooling
Every language ships a JSON parser in its standard library. XML requires a dedicated library, and XML's ecosystem tools — XSLT, XPath, XML Schema — are more powerful but far heavier.
Schemas
JSON Schema is now widely adopted for API contracts. It's expressive enough for the vast majority of use cases, and OpenAPI / AsyncAPI ecosystems assume it.
When XML still wins
- Mixed content: interleaved text and elements (SVG, XHTML, DocBook).
- Namespaces: multiple vocabularies in one document.
- Long-lived enterprise contracts where XSD, WS-* or SOAP are already the standard.
Bottom line
Default to JSON. Reach for XML only when you have a specific reason.