Industry standards
In the Gen AI / LLM space, two standards have emerged as the de facto choice in their domains:
A2A (v1.0, Linux Foundation) defines how agents integrate and communicate with their peers. It defines the interface of an agent, but not the agent itself.
MCP (2026-07-28 spec, finalizes today) defines how an agent uses tools. It defines the internal plumbing of an agent, but not the agent itself.
One nuance to be fair to both: MCP can also act as an agent's public interface, when an agent is exposed as an MCP server inside a single trust domain. So A2A covers the cross-organization contract, and MCP covers everything inside it. Either way, the conclusion stands: neither protocol defines what an agent is.
