A2A vs MCP
The short answer: they solve different problems and are meant to be used together. The A2A documentation puts it this way: MCP is vertical, it deepens a single agent. A2A is horizontal, it connects agents. This page also answers "MCP vs A2A", it is the same question.
Difference table
| Axis | MCP | A2A |
|---|---|---|
| Direction | Vertical: agent to tools and data | Horizontal: agent to agent |
| Official one-line framing | Deepens a single agent | Connects agents across a boundary |
| Participants | Host, client, server | Client agent, remote agent |
| Core objects | Tools, resources, prompts | Agent Card, task, message, part, artifact |
| Discovery | Client asks the server what it supports (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 to the client | Remote agent is opaque: no memory, plan or tools exposed |
| Transport | stdio and Streamable HTTP | HTTP(S), with streaming (SSE) and webhook push notifications |
| Message format | JSON-RPC 2.0 | JSON-RPC 2.0 in the documented binding (other bindings unverified) |
| Governance | Open-source standard (governance details unverified here) | Linux Foundation project (A2A docs also mention the Agentic AI Foundation; unverified which applies now) |
When to use which
Use MCP when
- An agent or AI app needs to call a function, read a file, or query a database.
- The call has well-defined inputs and outputs.
- You want one server to work with many AI clients.
Use A2A when
- The other party is an autonomous agent with its own reasoning, tools and policies.
- The work takes several turns or runs for a while, and you need status updates.
- The agents belong to different teams or vendors and should not see each other's internals.
Use both when
The official example is an auto repair shop. A customer talks to a shop manager agent, and a mechanic agent talks to a parts supplier agent: those are A2A conversations. The mechanic's diagnostic scanner and repair manual lookups are tool calls: those are MCP. Most multi-agent systems end up with this split.
Quiz: MCP, A2A, or both?
FAQ
- What is the difference between A2A and MCP?
- MCP standardizes how an AI application connects to tools, data sources and prompts (agent to tool). A2A standardizes how independent agents discover each other and collaborate on tasks (agent to agent). The A2A documentation calls MCP vertical and A2A horizontal.
- Is MCP vs A2A a real choice?
- Usually not. Both are meant to be used together: an agent can use MCP for its own tools and use A2A to hand work to other agents.
- Which one should I learn first?
- If your agent needs to call APIs, read files or query databases, start with MCP. If you need agents owned by different teams or vendors to cooperate on long tasks, look at A2A.
- Do A2A and MCP use the same wire format?
- Both use JSON-RPC 2.0 messages in their documented bindings, but the methods, objects and lifecycles differ. They are not interchangeable.
See it in motion: the live demo shows A2A messages and one MCP tool call side by side.