The Agentic Stack: Demystifying UCP, MCP, and A2A

In the early 1990s, the internet was a chaotic mess of competing standards until a unified "stack" emerged: TCP/IP for transport, HTTP for documents, and HTML for presentation. Once those layers were agreed upon, the web exploded.

Today, we are at a similar inflection point with Agentic AI.

We have incredible "brains" (LLMs like Claude, Gemini, GPT-4), but they are largely trapped in chat boxes. To build a true Agentic Web—where AI can autonomously work, collaborate, and buy things—we need a new infrastructure stack.

That stack is emerging right now, built on three critical acronyms: MCP, A2A, and UCP.

If you are a developer or architect, here is how these three layers fit together to power the next generation of software.

The Architecture of Agency

You can think of the "Agentic Stack" as three distinct layers of capability: Context, Delegation, and Execution.

Layer 1: MCP (Model Context Protocol)

"How the Brain talks to the Data."

A Large Language Model (LLM) is brilliant but isolated. It doesn't know about your local files, your database, or your company's internal wiki. It only knows what it was trained on.

MCP (Model Context Protocol) is the standard interface that solves this. It acts as a standardized USB port for AI models. Instead of writing custom "connectors" for every database, developers build an MCP Server. The AI client (like Claude Desktop or a custom agent) connects to it and instantly gains "read/write" access to that context.

Use Case: You ask an agent to "Fix the bug in auth.ts."
Without MCP: You have to copy-paste the code into the chat window.
With MCP: The agent requests access to your file system, reads auth.ts directly, understands the surrounding file structure, and proposes the edit.

Layer 2: A2A (Agent-to-Agent)

"How the Brain talks to other Brains."

No single AI agent can do everything. You might have a "Coder Agent" that is great at Python, a "Legal Agent" that understands contracts, and a "Travel Agent" that knows airline APIs.

A2A protocols define how these specialized agents discover each other, negotiate tasks, and hand off work. It is the "social layer" of the machine web.

Use Case: You run an e-commerce business.
The Flow: Your "Manager Agent" realizes you are low on stock. It pings the "Inventory Agent" to confirm. The Inventory Agent then pings the "Finance Agent" to approve a budget. Finally, the Finance Agent authorizes the purchase.
The Value: Instead of building one massive, monolithic "God AI," you build small, specialized agents that communicate via A2A standards.

Layer 3: UCP (Universal Commerce Protocol)

"How the Brain interacts with the Market."

This is the final mile. Once an agent has Context (MCP) and has coordinated with its team (A2A), it eventually needs to interact with the external world to do something—specifically, to buy, sell, or book.

UCP (Universal Commerce Protocol) is the standard for machine-driven commerce. It structures product data, inventory availability, and transaction logic so that agents can execute trades without human intervention.

Use Case: Your Travel Agent finds a flight.
Without UCP: The agent tries to navigate a human website (Expedia), gets stuck on a CAPTCHA, or hallucinates a price.
With UCP: The agent connects to the airline's UCP feed, sees the verified real-time seat availability, and executes a cryptographically signed booking request instantly.

The Full Picture

When you put these three together, you get a fully autonomous workflow:

User Request: "Plan and book a company retreat for 10 people."
MCP: The agent reads your company roster and budget from your local internal database.
A2A: The main agent delegates "Flights" to a Travel Agent and "Hotel" to a Hospitality Agent.
UCP: The Travel Agent uses UCP to find and purchase 10 tickets on United. The Hospitality Agent uses UCP to book 5 rooms at a Marriott.
Result: Done.

Conclusion

We are moving past the "Chatbot" era. We are building the Agentic Web.

If you are building AI applications today, stop building walled gardens. Start building complying with the Stack.

Expose your data via MCP.
Design your agents to speak A2A.
Publish your inventory via UCP.

The future belongs to the interoperable.