MCP and A2A solve different coordination problems. MCP gives an agent a structured way to use tools, resources, and prompts. A2A helps agents communicate about work. A useful architecture can use both, but it should keep their responsibilities distinct.

Keep local tool access behind MCP

Use MCP-style interfaces when an agent needs controlled access to a database, search service, CRM, calculator, file store, or other capability. Each tool should have a narrow schema, explicit permissions, validation, useful errors, and logs. The tool schema guide covers the contract an agent needs in order to call a tool predictably.

Use A2A for delegated work

Use agent-to-agent communication when another agent owns a distinct task, context, or capability. The calling agent should send a bounded request and receive a status, result, question, or refusal. The receiving agent should not inherit authority merely because another agent asked it to act.

Join them at an explicit boundary

A coordinator can use MCP to inspect approved tools and A2A to delegate a task to a specialist. Keep identity, trust, approval, data minimisation, and audit records at the boundary. The A2A task guide explains the lifecycle, while the MCP security guide covers tool-side risks.

• Authenticate each agent and tool independently.
• Pass only the context required for the delegated task.
• Require approval for consequential actions.
• Trace the original request through every hop.

The architecture is strongest when either side can be replaced without changing the business rules. Protocols carry messages and capabilities; the service still owns the policy.