MCP vs A2A: The Two Agent Protocols, Compared Honestly

MCP (Model Context Protocol) standardizes how an AI agent connects to tools and data — one agent, many capabilities; A2A (Agent2Agent) standardizes how independent AI agents discover, communicate and delegate work to each other — many agents, coordinating. They sit at different seams of the same stack, and the honest framing is complement, not competition.

This completes the comparison set we maintain: MCP vs API covers the layer below (protocol vs raw endpoints), MCP vs RAG covers the knowledge question, and this guide covers the layer above — what happens when the thing on the other end of the wire is not a tool but another agent.

If you want the MCP fundamentals first, start with what is MCP; the short version is enough for this guide: an MCP server exposes self-describing tools, resources and prompts, and any MCP client — Claude, ChatGPT, Gemini, IDEs — discovers and calls them at runtime.

A2A was announced by Google in April 2025 and donated to the Linux Foundation in June 2025, where it now lives as an openly governed project with a technical steering committee drawn from AWS, Cisco, Google, IBM, Microsoft, Salesforce, SAP and ServiceNow, and a v1.0 specification. Its job: let agents built by different vendors, on different frameworks, work together without custom integration.

The core concepts:

• The Agent Card — a machine-readable description an agent publishes: who it is, what skills it offers, how to reach it, how to authenticate. It’s the discovery primitive, playing a role analogous to MCP’s tool listing but at the level of whole agents.
• Tasks with a lifecycle — work is delegated as a task that moves through states (submitted, working, completed, failed), supporting long-running jobs, progress updates and artifacts, not just single request-response calls.
• Opaque collaboration — agents cooperate by exchanging messages and results without exposing their internal state, memory, or proprietary logic. Each side stays a black box, which is what makes cross-vendor cooperation commercially plausible.

The protocol is deliberately shaped for enterprise plumbing: it builds on familiar web standards, leans on standard auth, and assumes agents may belong to different companies with different trust levels.

The deepest difference is the last structural row: an MCP tool is predictable — same input, same behavior — while an A2A counterpart is an autonomous system that reasons, plans and can fail in novel ways. That’s why A2A invests so much in task lifecycle and status: delegating to an agent is managing a contractor, not calling a function.

Google’s own framing is that A2A and MCP are complementary layers, and the composed picture makes it obvious why:

The two protocols are not at the same maturity, and pretending otherwise helps nobody.

MCP is deployed. It has shipped clients from every major model vendor, an official registry, thousands of public servers, and real production traffic — including ours. When you build an MCP server today, there are immediate consumers for it.

A2A is well-backed but earlier. The Linux Foundation governance, the v1.0 spec and the steering-committee roster are genuine signals — this is how standards that last get run. But most multi-agent systems in production today are single-vendor (agents coordinated inside one framework, where an interop protocol is unnecessary), and cross-company agent federation — A2A’s headline use case — is still mostly pilots. The protocol is a bet on where the industry is going, not a description of where it is.

Three questions settle it:

1. 1Do your agents need capabilities? (Tools, data, systems to act on.) That’s MCP, and it’s almost certainly where you start — an agent with nothing to call has nothing to delegate either.
2. 2Do you run multiple agents from different vendors or frameworks that must cooperate? If they’re all inside one framework, its native orchestration is simpler. A2A earns its keep when the agents genuinely don’t share an implementation — different companies, different stacks.
3. 3Are you exposing an agent for others to use? Publishing an Agent Card makes your agent discoverable to A2A callers; exposing an MCP server makes your *capabilities* callable by anyone’s agent. Today the second has far more consumers, which is why our default advice is MCP first.

Where this points for businesses: the near-term, high-traffic seam is agents reaching into businesses for data and actions — and that seam is MCP-shaped. It’s the layer where the buyer-side future gets interesting too, which we explore in agentic commerce.