A2A Protocol Components

In today’s digital world, many systems rely on secure and efficient communication between different applications, services, and agents. The Agent-to-Agent (A2A) protocol plays a crucial role in enabling such communication by allowing software agents to interact directly and securely. A2A it as a method where one software agent (client) communicates with another agent (server) to exchange data, perform tasks, or trigger actions—all without human involvement. This makes A2A especially useful in automation, cybersecurity, and secure data sharing environments.

A2A Client

The A2A client is the initiating component in the A2A communication process. It acts like a messenger that prepares and sends a request to the remote agent or A2A server.

An application, service, or another AI agent that acts on behalf of the user to request actions or information from a remote agent. The client initiates communication using the A2A protocol

A2A Server – Remote Agent

The A2A server, also known as the remote agent, is the component that receives the request from the A2A client.

An AI agent or agentic system that exposes an HTTP endpoint implementing the A2A protocol.

It receives requests from clients, processes tasks, and returns results or status updates. Once the message is received, the server authenticates the request, processes it, and performs the desired action or responds with appropriate data. It plays a critical role in validating the source of the request, maintaining session security, and enforcing policies. The remote agent often operates on behalf of a specific service or endpoint that the client wants to access or control. The remote agent operates as an “opaque” system from the client’s perspective, meaning the client doesn’t need to know its internal workings, memory, or tools.

Agent Card

An Agent Card is a form of digital agent’s identity (name, description), service endpoint URL, version, supported A2A capabilities (like streaming or push notifications), specific skills it offers, default input/output modalities, and authentication requirements assigned to each agent involved in the A2A protocol.

• An Agent Card a JSON metadata document (e.g., agent.json) discoverable at a well-known URL, that describes an A2A Server.

It includes metadata such as the agent’s unique identifier, public key, and other profile information needed to establish trust. The card helps ensure that both the client and server recognize each other and communicate securely. In practice, the agent card is used during the authentication and encryption phases of communication.

Clients use the Agent Card to discover agents and understand how to interact with them securely and effectively.

Message

Message represents a single turn or unit of communication between an A2A client and the A2A server.

Server-Sent Events (SSE)

Server-Sent Events (SSE) is a technology used in A2A communication to push updates from the A2A server to the client in real-time. Unlike traditional request-response methods, SSE allows the server to send data automatically to the client as soon as an event occurs. This is especially useful when the A2A client needs to be notified about updates, acknowledgments, or completion statuses without continuously polling the server. SSE enhances the efficiency and responsiveness of the A2A protocol.