MCP vs A2A: Which Protocol Should Your Enterprise Bet On?

Every architecture review I sit in now asks the same question: MCP or A2A? It's the wrong question. They solve different problems — and most enterprises will end up running both.

Model Context Protocol (MCP) standardises how a model reaches tools and data: resources, tools, prompts, exposed once and consumed by any compliant LLM. Agent-to-Agent (A2A) standardises how agents talk to other agents: capability discovery via Agent Cards, task delegation, streaming results across vendors and frameworks. MCP is vertical — agent to its tools. A2A is horizontal — agent to peer agents. The mental model I give clients: MCP is the USB-C port; A2A is the network protocol.

If your problem is "our LLM needs governed access to internal systems" — document stores, databases, ticketing, trading data — MCP is the answer, and it's the more mature bet today. Build an MCP server once per system, enforce auth and audit at that boundary, and every model you adopt later plugs into the same servers. The kill feature for enterprises is the security chokepoint: one place to implement permissions, logging, and rate limits, instead of N bespoke integrations rotting in N codebases.

A2A matters the moment you have multiple autonomous agents that need to cooperate across team or vendor boundaries — your research agent delegating to a compliance agent built by another team, or a partner's agent negotiating with yours. Agent Cards give you discovery ("what can this agent do?"), and the task lifecycle gives you delegation with status streaming. If all your agents live inside one LangGraph application, you don't need A2A yet — in-process orchestration is simpler and faster. A2A pays off at organisational scale, not application scale.

Ask one question: is the boundary you're crossing a tool boundary or a trust boundary? Crossing into a system (database, SaaS API, file store) → MCP. Crossing into another autonomous decision-maker (another team's agent, a vendor's agent) → A2A. In a bank deployment we run, the document-intelligence agent uses MCP servers for core banking data, and exposes itself over A2A so the risk team's agent can delegate document checks to it. Vertical and horizontal, together.

The honest caveats: MCP's ecosystem is bigger and battle-tested; A2A is younger, and cross-vendor interop still has rough edges — version pinning and conformance tests are not optional. And neither protocol absolves you of the hard work: permissioning, evaluation, and observability are still yours to build.

Bottom line: adopt MCP now for every internal integration; pilot A2A where two genuinely independent agents must cooperate. Betting on one "winner" misreads what they are — TCP didn't kill USB.