WADL (Web Application Description Language) is an XML-based specification for describing HTTP-based web applications and RESTful services. It models resources, methods, request and response representations, and faults in a machine-readable form.
WADL
WADL (Web Application Description Language) is an XML-based specification for describing HTTP-based web applications and RESTful services in a machine-readable form. Submitted to the W3C by Sun Microsystems in 2009, it models the resources a service exposes, the methods available on each, the request and response representations, and the faults that can be returned. It was an early attempt to give REST the kind of machine-readable contract that WSDL gave to SOAP.
- XML-based description - The service contract is expressed as XML, describing resources, methods, and representations.
- Resource-centric model - Built around resources and the HTTP methods acting on them, matching the REST style it aimed to document.
- Machine-readable contract - Intended to drive client generation, documentation, and testing from a single definition.
- W3C Member Submission - Published as a W3C submission rather than a ratified standard, which shaped how far it spread.
In practice, WADL never achieved broad adoption — the community largely coalesced around Swagger and then OpenAPI as the machine-readable contract for REST APIs. I still see WADL in older enterprise and Java-ecosystem stacks, and it remains a useful historical marker for how the industry worked toward a shared API definition format. When it turns up today, the practical move is usually to convert it to OpenAPI so it can flow through modern documentation, governance, and agentic tooling.
Referenced on the API Evangelist blog
Where this standard shows up across sixteen years of my writing at apievangelist.com — how it fits into API design, governance, and the agentic turn.
Discovery Services for Common APIs
2011-05-21
The Swagger Specification
2014-05-29
