Capability · Comparison
MCP vs A2A Protocol
The Model Context Protocol (MCP, Anthropic) and the Agent-to-Agent Protocol (A2A, Google) are the two open protocols shaping agent interoperability in 2026. MCP standardises how an LLM connects to tools, data, and context sources — one model, many tools. A2A standardises how autonomous agents discover, invoke, and stream from other autonomous agents — many agents, interoperating. Different layers, not direct competitors.
Side-by-side
| Criterion | Model Context Protocol (MCP) | Agent-to-Agent Protocol (A2A) |
|---|---|---|
| Primary relationship | Model <-> Tool/Data | Agent <-> Agent |
| Originator | Anthropic (2024) | Google + partners (2025) |
| Transport | stdio, HTTP/SSE, streamable HTTP | HTTPS + JSON-RPC + SSE streaming |
| Discovery | Client configures servers | Agent Card (.well-known/agent.json) |
| Authentication | OAuth 2.1 recommended | OAuth 2.1, API keys, enterprise SSO |
| Streaming | Yes (responses + progress) | Yes — task streaming and multi-turn |
| Ecosystem | Broad — most IDE and LLM clients | Growing — Google, LangGraph, CrewAI, Agentforce |
| Typical use | Expose GitHub / docs / DB to Claude / ChatGPT / Gemini | Compose multi-vendor agent workflows |
Verdict
MCP and A2A are complementary layers of the same agent stack. MCP is for the inside of one agent — how your LLM reaches tools, files, databases. A2A is for the outside of one agent — how your agent talks to someone else's agent over the network. A full agent platform in 2026 typically speaks both: MCP inward to tools, A2A outward to other agents. Choose MCP when you need tool integration; A2A when you need agent composition across vendors.
When to choose each
Choose Model Context Protocol (MCP) if…
- You're building or consuming tools for an LLM to use.
- You want a standard way to expose APIs, files, or DBs.
- You need IDE-side integration (Claude Desktop, VS Code, Cursor).
- You want the broadest client support today.
Choose Agent-to-Agent Protocol (A2A) if…
- You're composing multi-agent systems across vendors.
- You need standardised agent discovery (Agent Card).
- You're building on Google Vertex AI / Agent Builder.
- You want long-running, streaming agent-to-agent tasks.
Frequently asked questions
Do MCP and A2A compete?
No — they're at different layers. MCP is for model-to-tool. A2A is for agent-to-agent. An A2A-exposed agent often uses MCP internally to reach its tools.
Which is more widely supported?
MCP, as of 2026 — adopted by Anthropic, OpenAI, Google, most IDEs, and a large ecosystem of community servers. A2A is newer but growing fast, especially inside Google's ecosystem.
Should I build on both?
If you're building a full agent platform, yes. Speak MCP to integrate tools and data sources. Expose A2A endpoints so other agents (internal or external) can call yours.
Sources
- Model Context Protocol — spec — accessed 2026-04-20
- A2A Protocol — Google announcement — accessed 2026-04-20