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:

1. agent card — capabilities metadata, discovery;
2. task lifecycle management — state machine (submitted/executing/requires input/completed/error), support for long tasks and streaming progress;
3. opaque interaction — exchange only tasks and artifacts, without revealing 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