XML
Definition.
XML: Extensible Markup Language, a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable.
In More Detail
XML predates JSON as the general-purpose data format and is more verbose, but it carries things JSON does not: attributes, namespaces, comments, and schema validation via XSD.
It survives where those features matter — SOAP APIs, publishing formats, government and banking integrations, and RSS. Sitemaps are XML too, which is the version most web projects still touch, this site included.
In Practice
I mostly encounter this now in the context of sitemap.xml files and legacy third-party API integrations — JSON is the default for anything new, but XML integrations still come up when connecting to older enterprise systems.
Related Terms
Browse the full software development glossary, or see the frequently asked questions.
If you are working out whether this applies to your own project, the case studies show where it turned up in real builds, services lists what I take on, and pricing gives the starting figures.
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