A2UI vs MCP-UI: Understanding the Protocol Landscape

TL;DR: MCP handles context (what the AI knows). A2UI handles presentation (what the user sees). They’re complementary, not competing.

[!NOTE] December 2025 Update: MCP has been donated to the Linux Foundation’s Agentic AI Foundation (AAIF), further solidifying its role as the industry standard for agent context.

The Confusion

With multiple “AI protocols” emerging in 2024-2025, developers are understandably confused. This article clarifies the landscape.

Protocol Overview

Feature	A2UI	MCP (Model Context Protocol)
Primary Purpose	UI Rendering	Context Injection
Data Flow	Agent → User	Data Sources → Agent
Output	Visual Components	Text/Structured Data
Security Focus	Prevent UI injection	Authorize data access

When to Use A2UI

A2UI shines when your agent needs to show something to the user beyond plain text:

Rich Data Display: Flight cards, restaurant listings, product catalogs.
Interactive Forms: Dynamic surveys, booking flows, multi-step wizards.
Data Visualization: Charts, maps, dashboards.

{
  "type": "flight-card",
  "props": {
    "airline": "TechAir",
    "departure": "SFO",
    "arrival": "NRT",
    "price": 1250
  }
}

When to Use MCP

MCP excels when your agent needs to know something:

Database Access: Query your PostgreSQL, Supabase, or Firebase.
File System: Read local documents, CSVs, PDFs.
API Integration: Connect to Salesforce, Jira, Notion.

The Synergy: Using Both Together

The most powerful agentic applications use both protocols:

[User Query] → [MCP: Fetch Data] → [LLM: Reason] → [A2UI: Render UI]

Example Flow:

User asks: “Show me my upcoming flights.”
MCP fetches flight data from the user’s calendar and airline API.
LLM processes and prioritizes the results.
A2UI renders a beautiful <FlightList /> component.

Security Model Comparison

A2UI: “Vending Machine” Approach

The client pre-registers allowed components.
The agent can only request from the approved menu.
Result: Zero risk of arbitrary code execution.

MCP: “Gated Access” Approach

Each data source has explicit permissions.
The user authorizes which sources the agent can access.
Result: Controlled data exposure.

Conclusion

Don’t choose between A2UI and MCP. Choose both for a complete agentic stack:

Layer	Protocol
Context (Input)	MCP
Presentation (Output)	A2UI