Declarative UI describes what an interface should render. A semantic app definition describes what the application is: its screens, data, workflows, roles, access rules, actions, deployment behavior, and runtime intent.
The difference matters because AI app development is moving from free-form generation toward structured intent. UI needs structure, but production applications need more than UI structure.
What is declarative UI?
Declarative UI lets a system describe the desired interface without sending arbitrary executable UI code. Google's A2UI project is a good example: agents can send UI layouts as messages, and a trusted client renders them using known components. Vercel Labs' json-render points in a similar direction by constraining generated UI to predefined components, actions, and schemas.
The benefit is clear. AI can create or populate an interface, but the host controls how that interface is rendered.
What is a semantic app definition?
A semantic app definition goes beyond the interface. It captures the meaning and operating model of the app: data model, record relationships, workflows, permissions, privacy rules, actions, integrations, environments, and release behavior.
That is the layer Buzzy focuses on. The UI is part of the definition, but it is not the whole definition.
Why is declarative UI not enough?
Declarative UI can make interfaces safer and more portable, but it does not automatically answer production questions:
Who can see each record?
Which workflow state is valid?
Which fields are private?
How do changes move from staging to production?
How do support teams pause or restrict the app?
Those questions require application semantics, not just UI semantics.
How do Google, Vercel, and Buzzy fit together?
Google A2UI is best understood as an agent-to-UI layer. Vercel json-render is best understood as a generative UI schema and rendering layer. Buzzy is best understood as a semantic application platform layer.
They are not the same category. They are signs of the same architectural shift: AI output needs structure before businesses can rely on it.
FAQ
Is semantic app definition just another name for declarative UI?
No. Declarative UI is about interface rendering. Semantic app definition includes UI, but also data, workflow, security, and lifecycle structure.
Why should enterprises care?
Because enterprise risk usually lives in data access, workflow behavior, integrations, and release control, not only in how a screen renders.
Where does Buzzy fit?
Buzzy fits when teams need the application itself to be defined, governed, secured, tested, and evolved, not merely rendered.