Dynamic metadata allows for metadata that can be configured for an application programming interface (API) after the API has shipped. Multiple entities can provide metadata for the same API or portions of an API. The metadata provided for an API can be set up for each application domain, allowing customization within a single process. Metadata can be provided in several ways, including traditional compiled code and declarative markup as well as databases and other more dynamic approaches. Metadata is separated from its runtime components, so that the metadata that is used by the runtime components can be changed. For example, metadata may be declared on the objects separately. The metadata is then tied back to the runtime components.