MCP vs A2A
They're not competitors — they connect different things. MCP connects an agent to its own tools and data. A2A connects one agent to a completely different agent it doesn't control. A system can use both at once: MCP for what it looks up or acts on directly, A2A for the other agents it hands work to.
What MCP does
Standardizes how an AI application connects to external tools and data, so a tool built once works with any MCP-compatible application without custom integration code for that specific pairing. Learn more: MCP.
What A2A does
Standardizes how one AI agent asks a completely different agent — built by another team, running on another framework, hosted somewhere you don't control — to do something for it, without custom integration code for that pairing either. Learn more: A2A.
Side by side
| MCP | A2A | |
|---|---|---|
| Connects | An agent to its own tools and data | One agent to a different, independent agent |
| Layer | Vertical — agent down to its resources | Horizontal — agent across to another agent |
| The other side is | A tool or data source | Another full agent, with its own reasoning |
| You control both ends? | Usually — you built or chose the tool | Not necessarily — the other agent is someone else's system |
Which one your problem calls for
Reach for MCP when your agent needs to look something up or act on a tool or data source directly — a database, a file system, a ticketing system's API.
Reach for A2A when the work needs to be handed to a genuinely separate agent you don't control the internals of — a different team's system, a different vendor's product, a partner's agent entirely. A travel-booking agent checking a hotel chain's own availability system is the textbook case: that's another company's agent, not a tool you'd write an integration for.
Neither replaces a subagent — that's delegation inside one system you already control, which is a simpler case than either of these protocols solves.
FAQ
If a system uses A2A to talk to another company's agent, does it still need MCP at all?
Usually yes, for a different part of the system — MCP handles that same agent's own tools and data, which A2A doesn't touch. The two operate on different layers, so using one doesn't remove the need for the other; a real system commonly runs both side by side.