A2A over MQTT

This is the specification and reference materials for A2A over MQTT, a broker-neutral profile for agent discovery and messaging.

Why MQTT?

MQTT is a lightweight and widely used protocol for IoT and edge computing. It is designed for unreliable networks and low bandwidth, making it a good choice for distributed agent systems that need discovery and message delivery across constrained links.

Introducing MQTT as a transport for A2A enables agent discovery via retained messages, broker-neutral request/reply conventions, and interoperable event delivery across systems that already use MQTT.

Features

The A2A over MQTT profile defines:

• Interoperable Agent Discovery: retained Agent Cards at a standardized discovery topic.
• Request/Reply Topic Conventions: consistent mapping for request, reply, and event topics.
• Minimal Security Guidance: optional trust metadata for Agent Cards without mandating broker internals.

Limitations

This profile is broker-neutral by design. It does not standardize broker internal architecture, UI, or administrative APIs. It also does not define end-to-end application semantics beyond the topic model and discovery behavior.