Syntax Verbosity

XML uses tags with opening and closing pairs, attributes, and namespaces that add significant overhead. A simple object in JSON might be 20 bytes; the equivalent XML representation could be 3-4x larger. For high-volume APIs, the size difference has real performance implications.

Document vs Data Orientation

XML was designed for documents — it supports mixed content, sophisticated namespace systems, and the ability to annotate data with attributes. These features make XML genuinely superior for document formats like HTML, DOCX, SVG, and XBRL. JSON handles data structures elegantly but has no equivalent for document markup.

Tooling and Ecosystem

JSON has extensive tooling across every programming language: JSON Schema, jq, JSONPath. XML has an equally extensive but more complex ecosystem: XPath, XSLT, XQuery, XML Schema, and SOAP. JSON tooling is generally simpler to learn and use.

When to Choose Each

Choose JSON for: REST APIs, configuration files, data storage in document databases, mobile app communication. Choose XML for: document formats (DOCX, SVG, XHTML), enterprise systems using SOAP or EDI standards, and when you need XPath querying capabilities.

Key Takeaway

JSON is the right default for data interchange in modern applications. XML remains necessary for document formats and enterprise systems with established XML standards.