A2A Protocol (Google)
Google's Agent2Agent (A2A) Protocol, announced April 2025, is an open specification for inter-agent task delegation, capability discovery, and message exchange. It defines AgentCards (capability manifests), Tasks, and Artifacts.
A2A complements the Model Context Protocol (MCP) — MCP wires an agent to its tools, A2A wires agents to each other. The two coexist in modern agent stacks.
Hive's MCP servers expose A2A-compatible AgentCards and emit Hive receipts for every cross-agent task.