# A2A vs MCP

Canonical page: https://agent-protocols-yxt.pages.dev/a2a-vs-mcp
Checked against official docs on 2026-10-20. Uncertain items are marked unverified.

Short answer: they solve different problems and are meant to be used together. The A2A documentation says MCP is vertical (it deepens a single agent) and A2A is horizontal (it connects agents). "MCP vs A2A" is the same question.

## Difference table

| Axis | MCP | A2A |
|---|---|---|
| Direction | Vertical: agent to tools and data | Horizontal: agent to agent |
| Participants | Host, client, server | Client agent, remote agent |
| Core objects | Tools, resources, prompts | Agent Card, task, message, part, artifact |
| Discovery | Client asks the server (server/discover, tools/list) | Client reads the remote agent's Agent Card |
| Typical interaction | Specific, often stateless function with structured input and output | Longer, multi-turn work with a task lifecycle |
| Visibility of the other side | Tool names, descriptions and schemas are listed | Remote agent is opaque |
| Transport | stdio and Streamable HTTP | HTTP(S), SSE streaming, webhook push notifications |
| Message format | JSON-RPC 2.0 | JSON-RPC 2.0 in the documented binding (other bindings unverified) |
| Governance | Open-source standard (details unverified) | Linux Foundation project (Agentic AI Foundation also mentioned; unverified) |

Read from A2A specification 1.0.0 and MCP protocol version 2026-07-28 pages. Specs change.

## When to use which

- Use MCP when an agent needs to call a function, read a file or query a database with well-defined inputs and outputs.
- Use A2A when the other party is an autonomous agent, the work takes several turns, and the agents should not see each other's internals.
- Use both when an agent delegates to a peer (A2A) and the peer uses tools (MCP). The official example is an auto repair shop: customer, shop manager and mechanic talk over A2A, diagnostic scanners and manuals are MCP tools.

## FAQ

**What is the difference between A2A and MCP?** MCP connects an AI application to tools, data and prompts. A2A connects independent agents so they can collaborate on tasks.

**Is it a real choice?** Usually not. They are complementary.

Sources: https://a2a-protocol.org/latest/topics/a2a-and-mcp/ , https://modelcontextprotocol.io/