Direct answer

Use MCP to connect an AI host or agent to tools, resources and context. Use A2A when independent agents need to discover capabilities, delegate work and exchange task results. A multi-agent system can use A2A between agents while each agent uses MCP to reach governed tools and data.

The boundary

user → coordinating agent ↔ specialist agent
          ↓ MCP                 ↓ MCP
   workspace context        domain tools

Google’s A2A announcement describes the protocol as complementary to MCP. Coordination and capability access have different identities, lifecycles and failure modes.

Decision matrix

QuestionMCPA2A
RelationshipAI client to serverAgent to agent
Main jobInvoke tools or contextDelegate tasks
Typical unitTool or resourceCapability and task
Can coexist?Yes; often the cleanest design

Avoid protocol-shaped architecture

Start with trust boundaries and jobs. Which component owns the user request? Which service owns data? Which actor may perform an action? Which results require provenance? Only then assign protocols.

An agent delegated through A2A should not inherit unrestricted access to every MCP server the coordinator knows. Give it the minimum capability and preserve actor and source identity through the chain.

The durable layer beneath both

Repeatedly ingesting the same business data for several agents is wasteful and difficult to govern. A shared context layer can normalize sources once, apply workspace policy and expose relevant evidence. Compare the layers in MCP vs RAG vs API.

Built for the next step

Keep data stable while agents multiply

SPYN3 is designed as the shared context layer beneath agent clients and workflows.

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About SPYN3

SPYN3 is AI-ready data infrastructure for technical solopreneurs and AI builders. It connects business data into a workspace-isolated knowledge layer and exposes it through a unified REST API and hosted MCP server, with permission-scoped access and source-aware returns. SPYN3 is currently in private beta; current capabilities and product direction are documented on the product facts page.

Sources

  1. Google Developers: A2A announcement — how A2A complements MCP. Verified 13 Sep 2026
  2. MCP project: 2026-07-28 release — stateless core, discovery, authorization and transition guidance. Verified 13 Sep 2026