Ironstead Group, LLC. The Agent Definition Language (ADL) provides a standard JSON-based format for describing AI agents. An ADL document declares an agent's identity, capabilities, tools, permissions, security requirements, data classification, and runtime configuration in a single, machine- readable artifact. ADL enables discovery, interoperability, deployment, and lifecycle management of AI agents across diverse platforms and runtimes. This document defines the structure of ADL documents, the semantics of their members, conformance requirements for implementations, and the registration of the application/adl+json media type.