MCP vs A2A: What Is the Difference?
MCP (the Model Context Protocol) connects a single agent to tools, data and context — it is how one agent reaches the world. A2A (Agent-to-Agent) is how independent agents discover and communicate with each other, including through agent cards. They are complementary layers, not competitors: MCP gives an agent hands; A2A lets agents find and talk to one another. A full stack uses both, plus an accountability layer neither addresses.
Different layers of one stack
It is a category error to ask which "wins." MCP is the substrate by which an agent uses a capability; A2A is the substrate by which agents locate and coordinate with each other. An agent can use MCP to reach a tool and A2A to hand work to a peer in the same task.
Both settle the capability layer and leave the accountability layer — who authorised this, who is responsible, what can be proven — out of scope by design. That vacated layer is where discovery, identity and verification standards, and this estate’s work, sit.
Related standards
Questions
Do I have to choose between MCP and A2A?
No. They address different problems and are commonly used together — MCP for tool and data access, A2A for inter-agent discovery and messaging.
Do MCP or A2A handle payments or identity?
Not primarily. They focus on capability and communication; payment, identity, authority and proof are separate layers that compose with them.
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By Michael Gord · published 2026-09-26 · part of the Agentic Encyclopedia. Dates are the day of publication; events are cited at their own dates.