AUP (Agentic UI Protocol) lets an application express what is shown and what actions are available. A runtime then renders the parts that fit its device capabilities, instead of treating one screen's pixels as the application itself.
A declaration can name content, structure, actions, and their relationships. It should not assume that a phone, television, watch, or voice-first device has the same controls or inputs.
The runtime exposes a capability set and uses it to determine which parts can be rendered and which inputs are available. The same semantic application can therefore be presented differently without claiming that every runtime supports every control.
See how a website presents AFS content through the Web Device.
Web Device: Declare a Website, Then Pick the Right PathDistinguish the protocol from the device that renders it.
UI Device