A2A Protocol

When interaction goes beyond an organization, a standardized protocol is needed: A2A (Agent2Agent, Google 2025, under the auspices of the Linux Foundation). Three elements: agent card (capabilities metadata, discovery), task lifecycle management (state machine: submitted/executing/input required/completed/error, support for long tasks and streaming progress), opaque interaction (exchange only tasks and artifacts – no revealing of prompts and reasoning traces). Location: MCP – agent with tools, A2A – agent with agent. Does not replace communication mechanisms, but a standardized layer on top of them when crossing trust boundaries.

Related: [MCP Protocol], [Decentralized model and handoff], [Inter-agent communication]