Agent2Agent (A2A) Protocol

The Agent2Agent (A2A) Protocol is an open standard introduced by Google that enables communication and interoperability between AI agents, regardless of the framework or vendor they are built on.

At Pydantic, we built the FastA2A library to make it easier to implement the A2A protocol in Python.

We also built a convenience method that expose PydanticAI agents as A2A servers - let's have a quick look at how to use it:

agent_to_a2a.py

from pydantic_ai import Agent

agent = Agent('openai:gpt-4.1', instructions='Be fun!')
app = agent.to_a2a()

You can run the example with uvicorn agent_to_a2a:app --host 0.0.0.0 --port 8000

This will expose the agent as an A2A server, and you can start sending requests to it.

See more about exposing PydanticAI agents as A2A servers.

FastA2A

FastA2A is an agentic framework agnostic implementation of the A2A protocol in Python. The library is designed to be used with any agentic framework, and is not exclusive to PydanticAI.

Design

FastA2A is built on top of Starlette, which means it's fully compatible with any ASGI server.

Given the nature of the A2A protocol, it's important to understand the design before using it, as a developer you'll need to provide some components:

• Storage: to save and load tasks
• Broker: to schedule tasks
• Worker: to execute tasks

Let's have a look at how those components fit together:

FastA2A allows you to bring your own Storage, Broker and Worker.

Installation

FastA2A is available on PyPI as fasta2a so installation is as simple as:

pipuv

pip install fasta2a

uv add fasta2a

The only dependencies are:

• starlette: to expose the A2A server as an ASGI application
• pydantic: to validate the request/response messages
• opentelemetry-api: to provide tracing capabilities

You can install PydanticAI with the a2a extra to include FastA2A:

pipuv

pip install 'pydantic-ai-slim[a2a]'

uv add 'pydantic-ai-slim[a2a]'

PydanticAI Agent to A2A Server

To expose a PydanticAI agent as an A2A server, you can use the to_a2a method:

agent_to_a2a.py

from pydantic_ai import Agent

agent = Agent('openai:gpt-4.1', instructions='Be fun!')
app = agent.to_a2a()

Since app is an ASGI application, it can be used with any ASGI server.

uvicorn agent_to_a2a:app --host 0.0.0.0 --port 8000

Since the goal of to_a2a is to be a convenience method, it accepts the same arguments as the FastA2A constructor.