A2A + MCP: The Protocol Stack That Will Replace Enterprise Integration

Two Protocols, One Architecture

If you've been tracking the agentic AI space, you've likely heard two protocol names repeated constantly: MCP (Model Context Protocol, from Anthropic) and A2A (Agent-to-Agent Protocol, from Google). The first reaction most architects have is: "Great, another standards war." But the reality is more interesting — and more useful — than a competition. MCP and A2A are complementary protocols solving different problems, and together they form the emerging protocol stack for enterprise agentic integration.

The simplest way to frame it: MCP is the agent's USB port — it connects an agent to tools, data sources, and services. A2A is the agent's LinkedIn — it connects an agent to other agents, enabling discovery, negotiation, and task delegation across organizational boundaries.

This article explains both protocols, how they complement each other, and how to architect systems that leverage both.

MCP: Connecting Agents to Tools

We've covered MCP extensively elsewhere, but here's the essential summary: MCP defines a standardized interface between an AI agent and external tools. An MCP server exposes capabilities (tools, resources, prompts) through a defined schema. An MCP client (embedded in the agent) discovers these capabilities and invokes them using structured requests.

The key innovation is universality: any MCP-compatible agent can use any MCP server without custom integration code. A database MCP server, a calendar MCP server, and a Slack MCP server all speak the same protocol. The agent doesn't need to know the implementation details — it just needs to understand the capability description.

MCP excels at vertical integration: connecting an agent deeper into an organization's systems. When your agent needs to query a database, send an email, access a CRM, or call an internal API, MCP is the protocol.

A2A: Connecting Agents to Agents

Google's Agent-to-Agent protocol addresses a different problem entirely: how do agents from different systems, organizations, or vendors communicate with each other?

A2A was introduced in 2025 with immediate support from over 150 enterprise partners, including Salesforce, SAP, Deloitte, Accenture, and MongoDB. The protocol is built around several key concepts:

Agent Cards

Every A2A-compatible agent publishes an Agent Card at a well-known URL (/.well-known/agent.json). This card declares the agent's capabilities, accepted input formats, authentication requirements, and pricing (if applicable). Agent Cards serve the same function as API documentation, but for autonomous agents: they allow other agents to discover what you can do, how to ask you to do it, and what it will cost.

Task Lifecycle

A2A defines a formal task lifecycle: submitted → working → input-required → completed / failed / cancelled. When Agent A sends a task to Agent B, both agents can track the task's state through this lifecycle. This is critical for enterprise use cases where tasks may take minutes or hours, not milliseconds — a procurement negotiation, a compliance review, or a complex data analysis.

Capability Negotiation

Before delegating a task, the requesting agent can query the target agent's capabilities to ensure the task is within scope. This prevents the common failure mode of sending a task to an agent that can't handle it, discovering the failure only after wasting time and tokens.

Streaming and Push Notifications

A2A supports both polling and streaming for task updates, plus push notifications for long-running tasks. This enables real-time coordination between agents without requiring them to maintain persistent connections.

Why You Need Both: A Procurement Workflow

The power of MCP + A2A becomes clear in a concrete scenario. Consider a procurement workflow at a manufacturing company:

Phase 1 — Internal Analysis (MCP): The company's Purchasing Agent receives a request to procure 10,000 units of a specific component. It uses MCP to access internal systems:

• Queries the inventory database (via MCP server) to check current stock levels.
• Queries the ERP system (via MCP server) to check production schedules and demand forecasts.
• Queries the budget system (via MCP server) to verify available procurement budget.
• Queries past purchase orders (via MCP server) to identify historical pricing and preferred suppliers.

Phase 2 — External Coordination (A2A): Armed with internal data, the Purchasing Agent now needs to engage suppliers. It uses A2A to:

• Discover available supplier agents by querying known supplier Agent Cards.
• Submit a Request for Quote (RFQ) task to three supplier agents simultaneously.
• Each supplier's Pricing Agent receives the task, checks inventory (using its own MCP connections to its own systems), and responds with pricing, availability, and lead times.
• The Purchasing Agent receives and compares all three quotes.

Phase 3 — Negotiation and Fulfillment (A2A + MCP): The Purchasing Agent selects the best offer and submits a purchase order task to the chosen supplier's agent via A2A. The supplier's agent processes the order using MCP to update its own order management system. Meanwhile, the Purchasing Agent uses MCP to update the company's procurement records, trigger a budget deduction, and notify the requesting team.

In this workflow, MCP handles all the intra-organizational tool access — querying databases, updating records, accessing internal systems. A2A handles all the inter-organizational agent communication — discovery, task delegation, negotiation, and coordination. Neither protocol alone could handle the full workflow.

The Convergence: Not Competition, Integration

One of the most common questions we hear is: "Will A2A and MCP merge?" The answer is nuanced. They're converging, but not merging.

On the MCP side, the 2026 roadmap explicitly includes an Agent-to-Agent Communication working group. This group is exploring how MCP's server interface could be extended to support agent-as-tool patterns, where one agent exposes itself as an MCP server that another agent can invoke. This would allow agent-to-agent communication within an organization using MCP's existing infrastructure.

On the A2A side, the protocol specification explicitly references MCP for tool access. An A2A agent's Agent Card can declare that it uses MCP servers, and the A2A task payload can include MCP context objects. This means an agent receiving a task via A2A can use MCP to execute the required tool operations.

The practical implication: MCP will handle agent-to-agent communication within a single organization's trust boundary, while A2A will handle agent-to-agent communication across organizational boundaries. This is analogous to how enterprises use internal service meshes for intra-organization communication and APIs/EDI for inter-organization communication.

Architectural Guidance

For enterprise architects adopting MCP + A2A, here's our recommended approach:

1. Start with MCP Internally

Get your agents connected to your internal tools via MCP. This delivers immediate value (faster integration, reduced connector maintenance) and builds the foundation for A2A adoption later. Every agent that speaks MCP is ready to participate in A2A workflows.

2. Publish Agent Cards Early

Even before you have external A2A use cases, publish Agent Cards for your internal agents. This creates a discoverable inventory of agent capabilities within your organization, makes internal agent-to-agent communication more structured, and prepares your infrastructure for external A2A integration when the time comes.

3. Design for Both Protocols at the Gateway Level

Your AI Gateway (or agent gateway) should understand both MCP and A2A traffic. MCP requests route to internal tool servers. A2A requests route to external agent endpoints. Both go through your security, logging, and governance layers. This unified gateway approach prevents the protocol-specific silos that plagued earlier integration architectures.

4. Implement Graduated Trust

MCP connections within your organization are high-trust (you control both sides). A2A connections with external agents are lower-trust (you don't control the other agent). Your architecture should reflect this: stricter validation, tighter permissions, more aggressive monitoring for A2A interactions compared to internal MCP connections.

5. Plan for the Convergence

As MCP adds agent-to-agent capabilities and A2A matures, the boundary between them will blur. Design your agent abstractions so that the communication protocol (MCP or A2A) is a transport detail, not a fundamental architectural decision. Your agents should communicate through a protocol-agnostic interface that can route via MCP or A2A as appropriate.

The Bottom Line

MCP and A2A aren't competing standards — they're complementary layers of the emerging agentic protocol stack. MCP connects your agents to your tools. A2A connects your agents to the world's agents. Together, they replace the brittle, bespoke integrations that currently connect enterprise systems with a standardized, discoverable, and governable protocol architecture. The enterprises that adopt both now will have a significant advantage as agent-to-agent commerce and coordination become the default mode of business-to-business interaction.