Demystifying Google’s Agent2Agent (A2A) Protocol in One Read

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Today, you’ve likely come across Google’s newly released open-source Agent2Agent communication protocol — in short, A2A.

Google officially stated that A2A is an extension of MCP (Multi-Agent Collaboration Protocol), aimed at enhancing coordination capabilities among large model Agents. While each Agent has powerful capabilities, they are isolated and can’t collaborate on their own. We’ve long needed to manually coordinate them. Even though AI helps partially, we still have to be “the glue.” Now with A2A, theoretically, Agents can collaborate without human intervention — all we need to do is sit back and enjoy the results.

Let’s walk through a real example to help you understand the power of A2A.

Let’s say you’re planning a weekend trip to the U.S. We need to first ask Agent A (the itinerary planner) to create the route, then Agent B (the booking assistant) to reserve flights and hotels, and finally Agent C (a local recommendation engine) to suggest what to do. These involve multiple back-and-forths, and you become the “manual middleware.” This form of agent orchestration requires human-driven logic and communication. A2A seeks to automate this entire multi-agent coordination process.

01 What is A2A?

Don’t get caught up in the name “Agent2Agent.” In essence, A2A is a standardized communication framework that enables AI Agents to talk to each other, much like HTTP or TCP/IP protocols do for computers.

Just like how internet protocols enable different websites and browsers to interact, A2A allows diverse Agents to communicate, coordinate, and even collaborate — regardless of the platforms or organizations they come from. It essentially builds a universal “inter-agent bridge” enabling seamless interaction across all AI Agents.

02 A2A Core Components Overview

A2A Technical Architecture & Key Concepts:

The A2A framework centers on a set of standardized technical components. These components ensure that different AI Agents can communicate, interoperate securely, and collaborate reliably.

02.1 Communication Protocol

A2A defines a standard protocol for exchanging agent messages, including syntax structure and transmission rules.

It covers:

Message encoding formats (e.g., JSON, Protobuf)

Metadata inclusion

Transport mechanisms like HTTPS, gRPC, WebSockets

These help ensure different intelligent agents can establish secure and structured message channels.

02.2 Agent Identity (Agent Card)

To support dynamic collaboration, A2A includes an “Agent Card” system that enables standardized self-identification. Each agent includes:

Identity details

Functional capabilities

Service interfaces (I/O parameters, intent)

Optional properties like cost, quality, and response latency

Diagram Breakdown:

Service Discovery → Locate available agents

Identity Declaration → Identify itself

Capabilities → Declare what it can do

Service Interface → Define input/output

Non-functional Properties → Cost, model type, etc.

02.3 Data Schema & Ontology

To guarantee accurate and consistent communication, A2A emphasizes clearly defined schemas and ontologies (data formats and structures). These specify what information is exchanged, its format, type, relationships, and expected values.

Shared ontologies ensure that different agents “speak the same language,” enabling effective interoperability.

02.4 Interaction Patterns

Beyond message exchange, A2A defines rich interaction models, enabling multi-turn cooperation in complex scenarios.

Examples:

Request/Response

Asynchronous Notifications

Publish/Subscribe

Negotiation

Delegation

Contract-Based Protocols

Diagram Labels:

Contract Protocol

Request–Response

Asynchronous Notification

Publish–Subscribe

Delegation

Multi-turn Dialogue

Negotiation

Trust & Security

Due to the sensitivity of AI agent interactions, A2A incorporates:

Authentication

Authorization

Encrypted transport (e.g., TLS/SSL)

Secure trust policies

These ensure agent ecosystems remain secure and stable.

A2A aims to help developers build open, standardized ecosystems where agents can discover, connect, and collaborate without constant re-coding or tight integration.

03 How Does A2A “Work”?

Here’s a simple step-by-step breakdown:

03.1 Agent Identity

Each agent uses an A2A “card” to announce its function (e.g., “I’m a flight booker,” “I do scheduling”).

03.2 Protocol Communication

The agents use A2A protocols to send/receive messages and relay mission details (e.g., dates, requirements).

03.3 Schema & Interaction

Agents use predefined schemas to confirm data accuracy and trigger the appropriate interaction pattern (e.g., request-response, publish-subscribe).

Diagram Labels:

Agent Identity

Mission

Planner Agent

Executor Agent

Example: Let the Agents Get to Work!

Flight Agent

Handles flight bookings

Hotel Agent

Handles accommodation reservations

Calendar Agent

Syncs to calendar

Let’s say you’re going on a business trip. You just tell your planning agent:

“Next week I need to fly to Silicon Valley for a trip. Please book flights and a hotel, and add the plan to my calendar.”

The planner uses A2A to trigger the following:

Calls the Flight Agent to book a flight

Calls the Hotel Agent to book a room

Calls the Calendar Agent to update the calendar

This all happens without you needing to manually orchestrate anything.

Last but Not Least

An isolated agent is just a glorified function.

Only when agents can collaborate, do we truly see their potential.

A2A is a big step forward in enabling agents to work together through standardized capability declarations, interface definitions, and secure communication.