A2A (Agent2Agent protocol)

An open protocol for one AI agent to hand a task to another agent, possibly from another vendor, and follow it until it is done.

Google introduced it in 2025 and it now sits under the Linux Foundation, like MCP. The difference: with MCP the other side is a tool that does one call and has no goals; with A2A the other side is an agent with its own model and state, and the unit of work is a task with a lifecycle (submitted, working, needs input, done). Agents publish a card describing their skills and how to authenticate.

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Related terms

MCP (Model Context Protocol): An open protocol for plugging tools and data into AI apps: write a server once, use it from any client.
Multi-agent system: Several AI agents with separate roles and contexts working on one task, usually coordinated by a lead agent or a fixed workflow.
Non-human identity (agent identity): Accounts, keys and tokens used by software rather than people: service accounts, API keys, CI tokens and, more and more, AI agents.

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