One diagram maps all the agent protocols: MCP, A2A, UCP, AP2, A2UI, AG-UI
rseroter · x · 2026-11-06
Metehan Yalcin (shared by rseroter) published a clear diagram mapping today's agent protocol stack from backend to frontend:
- MCP: gives agents access to tools and data
- A2A: agent-to-agent communication
- UCP: standardizes merchant discovery, catalog & checkout
- AP2: secures agent payments with signed mandates
- A2UI: agent outputs a JSON spec declaring which UI components to show, no code needed
- AG-UI: bidirectional, event-based state sync between agent backend and frontend (renderers: Lit, CopilotKit, Flutter)
The diagram organizes them as Backend (MCP/A2A/UCP/AP2) → UI definition (A2UI) → state streaming (AG-UI) → frontend renderers, clarifying where each standard fits in the agent ecosystem.
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