A2A and MCP, What Agent Interop Means for Your Architecture

Pull-quote: “Protocols standardize the seam, not the judgment. MCP tells an agent what a tool can do. It does not tell the agent whether calling it is a good idea.”

Two seams, two protocols

Enterprise agent architectures have exactly two seams that keep getting rebuilt from scratch: the seam between an agent and its tools, and the seam between one agent and another. MCP, the Model Context Protocol, standardizes the first: how a client discovers and invokes tools, resources, and prompts that a server exposes. A2A addresses the second: how agents advertise capabilities, delegate tasks, and exchange status and artifacts across team and vendor boundaries. The two are complements, not competitors, which the vertical-and-horizontal picture makes obvious.

                A2A: horizontal, agent ◄──► agent
        ┌────────────────────────────────────────────┐
        │  capability cards, task delegation,        │
        ▼  status, artifacts                         ▼
   ┌──────────┐                                ┌──────────┐
   │ Agent A  │                                │ Agent B  │
   │ (yours)  │                                │ (vendor) │
   └────┬─────┘                                └────┬─────┘
        │ MCP: vertical, agent ──► tools            │ MCP
        ▼                                           ▼
   tools · data · prompts                     its own tools

What each standardizes, and what neither does

The right column is the post. Neither protocol decides whether a delegation is wise, whether a returned artifact is correct, or what a partner agent is allowed to see. Interop standards move integration cost, and that is genuinely valuable: one MCP server replaces five bespoke connectors, and one A2A surface replaces a pile of point-to-point agent bridges. But a protocol-shaped hole remains where governance goes. An agent card is a claim, not a credential. Treat a remote agent the way you treat a remote service: authenticate it, scope it, budget it, and log every exchange as if you will be asked about it later, because in a regulated deployment you will.

A sober adoption order

1. Put MCP at your own tool seam first. This pays immediately, inside your own walls: every internal capability behind one contract, so any client, agent, IDE, or script reaches the same governed surface. The pattern that works is a thin application at the edge with the engine behind an MCP contract, so the next client costs a registration instead of an integration.
2. Treat A2A as an external seam, adopted when a real counterparty exists. The standard earns its keep at organizational boundaries, where you cannot dictate the other side’s stack. Do not rebuild internal orchestration around it speculatively; internal handoffs inside one runtime do not need a wire protocol between them.
3. Gate both behind your policy layer. Protocol adoption must not widen authority. The gateway that enforces identity, scopes, and budgets sits in front of the standard seam exactly as it sat in front of the bespoke one.
4. Log at the seam. The protocol gives you a clean place to record every capability advertised, every task delegated, every artifact returned. That log is your audit story when agents span vendors.

What changes for architecture reviews

The interesting shift is organizational. Once agent capabilities are advertised over standard seams, “which systems talk to which” becomes a catalog question instead of an archaeology project. Architecture review stops asking how the integration works and starts asking the better questions: who authorized this capability, what budget does it run under, and who is accountable for the artifact it returns.

Closing

MCP standardizes how agents reach tools; A2A standardizes how agents reach each other. Adopt the first at your own seams now, the second when a real external counterparty appears, and keep governance in front of both. The protocols move integration cost. Judgment, budgets, and accountability were never in scope, and they remain your architecture.