A2A-over-MQTT Python SDK

Python SDK for the A2A-over-MQTT protocol: build agents and clients that communicate via MQTT using the A2A (Agent-to-Agent) protocol.

Install

pip install a2a-over-mqtt

Or with uv:

uv add a2a-over-mqtt

Quick start

Build a responder (agent)

import asyncio
from a2a_over_mqtt import MqttConfig, TopicSpace, Responder, build_card, A2ARequest

class MyAgent(Responder):
    async def on_request(self, request: A2ARequest, stream) -> str:
        await stream("thinking...")
        return f"You said: {request.text}"

async def main():
    mqtt = MqttConfig(host="localhost", port=1883)
    topics = TopicSpace(org="myorg", unit="default")
    card = build_card(
        name="Echo Agent",
        description="Echoes back whatever you send",
        url="mqtt://localhost:1883",
    )

    agent = MyAgent(
        agent_id="echo",
        mqtt=mqtt,
        topics=topics,
        card=card,
    )
    await agent.run()

asyncio.run(main())

Send a request (client)

import asyncio
from a2a_over_mqtt import MqttConfig, TopicSpace, Requester, A2ARequest

async def main():
    mqtt = MqttConfig(host="localhost", port=1883)
    topics = TopicSpace(org="myorg", unit="default")
    requester = Requester(mqtt, topics)

    req = A2ARequest(text="Hello, agent!", request_id="req-1")
    async for kind, content in requester.stream("echo", req.to_json(), "corr-1"):
        print(f"{kind}: {content}")

asyncio.run(main())

API overview

Configuration

• MqttConfig(host, port, tls, username, password): MQTT broker connection parameters. Frozen dataclass.
• TopicSpace(org, unit): A2A topic namespace. Provides .request(), .reply(), .discovery(), .event() methods.

Protocol (pure, no I/O)

• A2ARequest / A2AResponse: JSON-RPC 2.0 message types with serialization.
• make_status_event() / make_artifact_event(): Build streaming response messages.
• classify_reply(data): Parse a reply into (kind, content) tuples.
• validate_a2a_request(payload, response_topic, correlation): Validate inbound requests. Returns A2ARequest or ValidationError.

Discovery

• build_card(name, description, url, ...): Build a spec-conformant A2A Agent Card.
• parse_card(payload): Parse a card from JSON bytes or string.

High-level

• Requester: Send requests and stream replies with configurable retry/timeout.
• Responder: Abstract base class for agents. Implement on_request(), call run(). Handles the full protocol lifecycle: ack, streaming, artifact, terminal status, deduplication, cancellation, and LWT.

Development

uv sync
uv run python -m pytest tests/ -v

Build and publish

uv run python -m build
uv run twine upload dist/*