Format the source with the XML Formatter, then use the XML to JSON Converter to inspect attributes, repeated elements, CDATA, and nested output locally.
XML and JSON are both text representations of structured data, but they were designed around different mental models. JSON looks like the objects and arrays used in application code. XML is an ordered document tree with elements, attributes, namespaces, and text nodes. The right choice depends on the data shape and the guarantees consumers need.
1. The decision in one minute
Use JSON for new object-shaped web APIs, browser applications, and configuration that maps directly to code. Use XML when you need document-oriented markup, namespaces, XSD validation, mixed content, or compatibility with an established enterprise integration.
| Need | Usually better fit | Reason |
|---|---|---|
| REST response with objects and arrays | JSON | Direct mapping to common language types |
| Long-lived document with markup | XML | Elements, attributes, order, and mixed content |
| Multiple vocabularies | XML | Namespaces make ownership explicit |
| Small browser payload | JSON | Less syntax and common native parsers |
2. The data models are not identical
JSON has objects, arrays, strings, numbers, booleans, and null. XML has elements and attributes, plus namespaces, text nodes, comments, and declarations. An automatic XML-to-JSON mapping is therefore an opinionated design, not a universal truth.
<user id="42" role="admin">Ada</user>
{
"user": {
"@attributes": { "id": "42", "role": "admin" },
"#text": "Ada"
}
}The mapping above keeps metadata and text visible. Choose and document a convention before different teams consume the output.
3. Feature comparison
Validation
JSON Schema describes JSON values with types, required properties, patterns, and composition. XML Schema can validate elements, attributes, namespaces, order, and document constraints. A schema language helps only when the pipeline actually runs validation.
Namespaces, order, and repetition
XML namespaces prevent vocabularies from colliding. XML child order can be meaningful in a schema. JSON arrays preserve order, but object member order should not carry business meaning. Repeated XML elements should normally become arrays; a mapper that emits an object for one item and an array for many creates an unstable contract.
Comments and mixed content
XML can interleave text and child elements. Standard JSON cannot contain comments and has no mixed-content model. If markup is part of the data, flattening it may lose meaning.
4. APIs and integration
JSON is the common default for new HTTP APIs because most languages provide convenient parsers. The API still needs decisions about dates, numbers, unknown fields, errors, and pagination. XML remains important in SOAP, publishing, financial messaging, shipping, identity, and government systems.
Do not convert an XML integration merely because JSON is fashionable. Existing contracts, signatures, validators, and vendor tools may be more valuable than a smaller payload. Supporting both formats requires semantic equivalence tests, not just two serializers.
5. A safe migration
- Inventory namespaces, attributes, CDATA, mixed content, repeated elements, comments, and empty tags.
- Write a mapping document with examples for every special case.
- Choose stable names for attributes and text, such as
@attributesand#text. - Define whether one element and many elements always become an array.
- Preserve namespace URIs when local names can collide.
- Compare semantic values in fixtures rather than only comparing pretty-printed text.
- Run original XML validation and new JSON validation during the transition.
The local converter is useful for inspecting structure without uploading a payload. It is not a replacement for contract tests.
6. Conversion failure modes
- Attributes disappear: the mapper emits child elements only.
- Repeated elements change shape: one item becomes an object while many become an array.
- Text nodes are lost: mixed content needs an explicit text key.
- Namespaces collide: prefixes can differ while URIs are equal, or match while URIs differ.
- Empty elements change meaning: empty string, null, missing, and empty object are different values.
- Numbers become strings: XML text has no JSON number type without a rule or schema.
Test a representative payload, an empty payload, repeated records, and an optional field. Most mapping bugs hide in those cases.
Conclusion
JSON is usually simplest for new object-shaped APIs. XML remains better when document structure, namespaces, validation, or ecosystem compatibility are central. Select based on the contract and its consumers, then document any mapping between formats.
Frequently Asked Questions
- Is JSON better than XML?
- Not universally. JSON is simpler for object-shaped APIs; XML is stronger for documents, namespaces, and established schema workflows.
- Can XML attributes become JSON fields?
- Yes, but define a stable mapping such as an @attributes object.
- Does JSON support comments?
- Standard JSON does not support comments.
- When should I keep XML?
- Keep it when consumers need XSD, namespaces, mixed content, or XML-specific tooling.
- Does XML preserve ordering?
- XML is an ordered document tree; JSON arrays preserve order, but object member order should not carry meaning.
- Is conversion lossless?
- Not automatically. Attributes, namespaces, mixed content, and repeated elements require explicit handling.