XML (Extensible Markup Language)
A structured text format for encoding documents and data, still used in configuration files, RSS feeds, and enterprise systems.
XML is a markup language that uses tags (like HTML) to structure data. Before JSON took over, XML was the default format for web APIs, configuration files, and data exchange. You will still encounter it in RSS feeds, SVG files, Android manifests, Maven configs, and SOAP APIs.
An XML document wraps data in opening and closing tags: <name>Alice</name>. Tags can be nested, and attributes can be added: <user role="admin">. Unlike JSON, XML supports comments, namespaces, and schemas for strict validation.
For vibe coders, XML shows up most often in SVG graphics, sitemap.xml files, and legacy integrations. Most modern APIs use JSON, but knowing XML exists and being able to read it helps when you encounter older systems or configuration formats that AI tools can help you convert.