A2A vs MCP
A2A and MCP are complementary protocols, not competitors. MCP (Model Context Protocol) connects one AI agent to its tools and data sources; A2A (Agent2Agent) connects agents to each other, so they can delegate tasks and return results across teams, frameworks, and companies. Most multi-agent systems end up using both.
What MCP covers
MCP, introduced by Anthropic, standardizes how an AI application reaches its tools. An MCP server exposes tools, resources, and prompts; the agent connects and calls them mid-task. The relationship is vertical: one agent, its capabilities. The agent is always the one asking, which is why MCP vs webhooks is really a pull-vs-push comparison.
What A2A covers
A2A, introduced by Google in April 2025 and donated to the Linux Foundation that June, standardizes the horizontal relationship: peer agents delegating work to each other. Each agent publishes an agent card, a JSON document describing its skills, endpoints, and auth requirements. A client agent reads the card, sends a task, and tracks it through a defined lifecycle from submitted to completed, failed, or canceled, including states where the task pauses for input.
Results come back three ways: a plain response for quick tasks, Server-Sent Events for streaming, or push notifications, where the remote agent POSTs updates to a webhook URL the client registered. That last mode is what makes an agent handoff survive tasks that run for hours.
The comparison
| MCP | A2A | |
|---|---|---|
| Connects | An agent to tools and data | Agents to other agents |
| Relationship | Vertical (capabilities) | Horizontal (delegation) |
| Introduced by | Anthropic | Google, now Linux Foundation |
| Discovery | Client configures known servers | Agent cards |
| Long-running work | Tasks extension, webhook delivery planned | Task lifecycle with push notifications |
| Typical question | "What can this agent use?" | "Who can do this for me?" |
The boundary blurs in practice. You can wrap an agent in an MCP server and call it like a tool, and plenty of teams do. The rule of thumb: if the callee is a dumb capability that answers instantly, MCP fits; if it's an autonomous peer that works over time and might need to come back with questions, that's what A2A's task model was built for.
Where they combine
A typical setup uses both layers at once: a coordinator agent receives a request, uses MCP to query internal data, then uses A2A to hand subtasks to specialist agents, each of which uses its own MCP servers to do the work. Results flow back over A2A push notifications.
Both protocols land on the same mechanism for async results: an HTTP POST to a registered URL. A2A has push notifications today, and MCP's tasks extension is adding webhook delivery. Neither spec covers retries, signing, or delivery observability, the operational layer [Svix]https://www.svix.com/?utm_source=resources&utm_medium=content) provides. Agent to agent communication covers the full set of mechanisms underneath both protocols.
Frequently asked questions
Do I need both A2A and MCP?
For a single agent with tools, MCP alone is enough. Once multiple autonomous agents delegate work to each other, especially across teams or organizations, A2A adds the discovery, task lifecycle, and async delivery that MCP does not cover. Multi-agent systems commonly use MCP within each agent and A2A between them.
Is A2A a replacement for MCP?
No. Google positioned A2A as complementary to MCP from the start: MCP connects an agent to capabilities, A2A connects agents to peers. The protocols even converge on the same webhook pattern for delivering results of long-running work.
Can an agent be exposed over both A2A and MCP?
Yes, and it is common. The same agent can publish an A2A agent card for peer delegation and also be wrapped as an MCP tool for clients that just want a synchronous answer. The A2A surface earns its keep when tasks are long-running or need multi-turn interaction.
Ready to send webhooks?
Svix handles signing, retries, rate limiting, and delivery observability for the webhooks you send to your users, so your team can stay focused on your product.
Start sending webhooks with Svix or read the build vs. buy analysis