A2A vs MCP: What's the Difference?

April 18, 2025 · Sarah Chen

April 28, 2025 · Sarah Chen

If you've been exploring modern agent systems, you've probably come across two key concepts: A2A (Agent-to-Agent) Protocol and MCP (Message Control Protocol). While they might seem similar at first glance—both deal with how digital agents communicate—their roles and responsibilities are actually quite different.

Let's break it down in simple terms.

A2A: The Language Agents Speak

The A2A Protocol defines how agents interact with each other. It's like a common language and set of rules that lets agents:

• Discover each other
• Understand shared tasks
• Negotiate intent
• Exchange structured messages
• Execute and coordinate actions

Think of it like the grammar and structure of a conversation. It ensures everyone is speaking the same way and can understand each other—no matter where they come from or what they do.

It focuses on what needs to be said and done between agents to get work done collaboratively.

MCP: The Dispatcher Behind the Scenes

The Message Control Protocol (MCP), on the other hand, handles how messages are transmitted and routed. It's more about the logistics of the conversation:

• Making sure messages get to the right place
• Controlling flow, retries, and timeouts
• Managing queues and delivery guarantees
• Handling session-level concerns like authentication and tracing

So while A2A is about the meaning and intent of the interaction, MCP is about making sure that interaction gets where it needs to go, safely and efficiently.

It's like a mail delivery system for the agents' conversations—delivering the letters reliably, while A2A defines what those letters should contain.

Real-World Analogy

Imagine you're sending a business proposal to a partner:

• A2A is the structure and tone of your proposal—what you say, how you ask, and what you expect.
• MCP is the delivery method—whether it's email, courier, or digital signature—and making sure it gets delivered properly.

You need both to make the interaction successful. If your message never arrives (bad MCP), or if your message is confusing (bad A2A), the task fails either way.

Why Not Just Use One?

Because these two protocols solve different problems.

• A2A focuses on intent and interoperability: helping agents work together meaningfully
• MCP focuses on delivery and control: making sure messages don't get lost or delayed

By separating the two, developers can:

• Swap out MCP implementations (e.g. HTTP, WebSockets, P2P transport)
• Keep the A2A logic clean and focused on the job agents are trying to do
• Maintain more flexible and scalable architectures

Summary

Together, A2A and MCP form the backbone of intelligent, agent-based systems. One ensures agents speak the same language, the other ensures they stay connected.

If you're building with agents, you'll want to understand both—and design your stack so they work hand in hand.