Comparison
JSON vs XML: the practical guide
JSON or XML for your API, config, or data feed? A practical side-by-side covering size, speed, tooling, validation, and when XML is still the right answer.
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TL;DR
Default to JSON. Choose XML only when you need strict schema validation (XSD), mixed content (documents with markup), or interop with industries that haven't migrated (banking ISO 20022, healthcare HL7, legal filings, SOAP).
Option A
JSON
Lightweight, JavaScript-native
Option B
XML
Schema-validated, enterprise-grade
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Side-by-side
| Dimension | JSON | XML |
|---|---|---|
| Payload size | Smaller (no closing tags) | ~30% larger on average |
| Parse speed | Very fast | Slower (DOM/SAX overhead) |
| Schema validation | JSON Schema (good) | XSD (excellent, mature) |
| Comments | None | Supported (`<!-- -->`) |
| Attributes | No distinction | First-class |
| Mixed content | Awkward | Native |
| Querying | JSONPath (basic) | XPath / XQuery (powerful) |
| Namespaces | None | Supported |
| Tooling | Modern & broad | Enterprise & deep |
| Best for | APIs, config, logs | Docs, contracts, compliance |
Why JSON won the web
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Where XML still shines
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Industries where XML is the standard
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Size and performance, measured
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Can I use both?
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Frequently asked questions
Is XML dead?
No. It's no longer the default for new public APIs, but trillions of dollars of transactions move through XML every day in banking, healthcare, and compliance. It's boring, stable, and extremely well-tooled.
Which is more secure?
JSON parsers don't load external entities, so they're immune to XXE (XML external entity) attacks — still one of the top OWASP threats. If you must parse XML from untrusted sources, disable DTDs and external entities in your parser config.
Which is easier to write by hand?
JSON, slightly. The braces and quoting get repetitive but it's denser. XML's verbosity feels heavy but its structure is self-documenting — closing tags tell you exactly what element you're in.
Which has better streaming?
XML has mature streaming APIs (SAX, StAX) that process documents without loading them into memory. JSON streaming exists (JSON Lines, ijson, jq --stream) but is newer and less standardized.