MCP vs A2A: Which Agent Protocol Do You Need?
Compare MCP and A2A, how they differ, when to use each protocol, and why agent-ready systems often need both tool access and agent coordination.
Updated May 17, 2026
MCP and A2A solve different problems. MCP connects an AI agent to tools, data, and resources. A2A connects one agent to another agent so they can exchange tasks and results. If your system only needs tool access, MCP may be enough. If multiple agents must coordinate work across vendors or services, A2A becomes relevant too.
The core difference#
Google describes A2A as an open protocol for agent interoperability and explicitly says it complements MCP. The official MCP architecture docs describe MCP as a way for clients and servers to exchange tools, resources, and prompts.
Primary sources:
- Google Developers Blog: Announcing A2A
- MCP architecture overview
- Google Developers Blog: A2A donated to Linux Foundation
| Question | MCP | A2A |
|---|---|---|
| Who talks to whom? | Agent client to tool server | Agent to agent |
| Main object | Tool, resource, prompt | Task |
| Best for | Accessing capabilities | Coordinating work |
| Discovery model | Tool schemas | Agent capabilities and task handling |
| Typical example | “Get order status” | “Ask travel agent to plan itinerary” |
Use MCP when#
MCP is the better first choice when an agent needs to:
- read documents
- call database-backed tools
- fetch product information
- trigger bounded actions
- work with one system’s capabilities through a consistent interface
That is why MCP appears so often in the execution layer and in the MCP vs API guide.
Use A2A when#
A2A is useful when:
- one agent delegates work to another
- different vendors’ agents need to collaborate
- a task has its own lifecycle and status
- the result may take time
- multiple specialists contribute to one workflow
Examples:
- procurement agent delegates tax analysis
- travel agent delegates hotel selection
- support agent delegates identity verification
- orchestration agent coordinates fulfillment, payment, and messaging
The multi-agent AEO guide covers why this matters once workflows stop being single-step calls.
Why many systems need both#
| Layer | Likely protocol |
|---|---|
| Agent reads or executes a tool | MCP |
| Agent delegates a job to another agent | A2A |
| Agent pays for a service | x402, UCP, ACP, or another payment layer |
| Agent discovers important site docs | llms.txt, internal links, structured pages |
A travel system might expose hotel availability through MCP, use A2A to collaborate with a flight-booking agent, and use a commerce or payment protocol for checkout. The protocols stack; they do not need to compete.
Architecture example#
Imagine a B2B procurement workflow:
- A coordinator agent receives a buying request.
- It uses A2A to ask a security-review agent for vendor risk analysis.
- The security-review agent uses MCP tools to read policy docs and control evidence.
- The coordinator uses MCP again to query pricing and integrations.
- Another protocol handles the approved transaction.
If you use only MCP, you can expose tools. If you use only A2A, the agents can exchange jobs but still need tools underneath. Mature systems need both layers.
Decision table#
| If you need… | Start with… |
|---|---|
| One agent calling your product tools | MCP |
| Cross-company agent collaboration | A2A |
| Task status and delegation | A2A |
| Fastest path to useful integration | MCP |
| Multi-agent workflow orchestration | MCP plus A2A |
FAQ#
Is A2A a replacement for MCP?#
No. Google’s own announcement says A2A complements MCP.
Which protocol should a small business implement first?#
Usually MCP, because it exposes immediately useful tools and data. Add A2A when delegation between agents becomes a real workflow need.
Does A2A replace Agent Cards?#
No. Agent capability discovery and protocol exchange are related but separate concerns. See the Agent Cards guide.
Can MCP and A2A share the same business logic?#
Yes. The same internal services can power MCP tools and A2A task handlers through different protocol surfaces.
Bottom line#
MCP gives agents tools. A2A gives agents peers. If your roadmap moves from single-agent actions to coordinated multi-agent workflows, plan for both.