MCP vs A2A: what is the difference?
Updated · DBShifts
Short answer
MCP (Model Context Protocol) connects an AI agent to tools and data: the agent calls a tool and gets a result back. A2A (Agent2Agent) connects agents to other agents: one agent sends another a task, and that agent decides how to do it, often with its own tools. Most multi-agent systems use both, so both need access rules.
Key facts
- MCP is agent-to-tool; A2A is agent-to-agent.
- In MCP the model calls tools that a server exposes; in A2A an agent hands a task to another agent that works out how to complete it.
- An A2A agent describes itself with an Agent Card: its skills, its endpoint and how callers authenticate.
- A2A was introduced by Google in April 2025 and is now developed as an open project under the Linux Foundation.
- Neither protocol decides what data may pass between the parties; that is policy you add on top.
In the glossary:A2A (Agent2Agent protocol)
What each protocol is for
MCP gives a model tools, resources and prompts from a server. The model stays in charge: it picks the tool, supplies the arguments and reads the result.
A2A is for delegation between agents that each have their own model, tools and instructions. The caller sends a message, the receiving agent runs a task — which can be long-running and stream progress — and returns artifacts. The caller does not see how the work was done.
How they fit together
A typical chain: a chat app sends a task over A2A to a support agent, which calls a billing agent over A2A, which reads the customer's invoices through an MCP server in front of the database. One user request becomes several hops across both protocols.
Where the security risks differ
MCP risks centre on tools: over-broad tools, unchecked arguments, and descriptions or results that carry instructions for the model. A2A adds delegation risks: data handed to an agent that should not see it, the original user's identity lost after the first hop, and agents calling each other in loops. Both need caller authentication, least privilege, data rules on every hop and an audit trail.
Checklist
- 1
Inventory both the MCP servers and the A2A agents in use
- 2
Write a rule for each caller-to-target pair, with deny as the default
- 3
Mask or block sensitive data on every hop, in both directions
- 4
Carry the original requester's identity through every hop
- 5
Limit chain depth, repeated calls and fan-out
- 6
Trace every hop of a chain under one ID
Common mistakes
Treating them as competing standards
They solve different problems. Choosing one does not remove the need for the other once agents both use tools and delegate to each other.
Securing the tools but not the agents
An agent that is allowed to read a table can pass what it read to any agent it calls. Controls on the tool alone do not cover the handoff.
How DBShifts does it
- DBShifts Agent Mesh governs both: agent-to-agent calls over A2A and agent-to-tool calls over MCP, through one set of default-deny rules.
- Data is masked or blocked by class on every hop in both directions, and each hop carries a signed chain token naming who started the chain and every agent since.
- DBShifts Agent Gateway is the MCP server for the databases those agents read from.
Questions people also ask
Do I need A2A if I already use MCP?
Only if agents delegate work to other agents. A single agent calling tools needs MCP alone; once agents hand tasks to each other, A2A is the standard way to do it.
Can one agent use both protocols?
Yes, and most do: an agent receives tasks over A2A and carries them out with MCP tools.
Related questions
Give AI agents data access you can defend
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