COMPLETE guide to agent-to-agent communication — A2A, MCP, ACP & ANP protocols explained, compared, and mapped to real use cases. Learn which protocol to use and when.
Frequently Asked Questions
What is agent-to-agent (A2A) communication?
Agent-to-agent communication is the ability for one AI agent to discover, invoke, and exchange structured data with another agent — without a human in the loop. The A2A protocol, introduced by Google in April 2025, is the leading open standard for this, using Agent Cards for capability discovery and JSON-RPC over HTTPS for message transport.
What is the difference between MCP and A2A?
MCP (Model Context Protocol) connects an agent to tools and data sources — it is a vertical connection between an agent and its environment. A2A connects agents to other agents — it is a horizontal, peer-to-peer connection. They are complementary, not competing. See our [full MCP vs A2A comparison](/blog/mcp-vs-a2a/) for more detail.
How do AI agents communicate with each other in practice?
In A2A, a client agent sends a task to a remote agent's endpoint using JSON-RPC 2.0 over HTTPS. The remote agent processes the task and returns artifacts (text, files, structured data). For long-running work, Server-Sent Events (SSE) stream progress back in real time. The client agent first reads the remote agent's Agent Card — a JSON manifest listing its capabilities, auth requirements, and endpoint URL.
What protocols do AI agents use to communicate?
The four major protocols are: MCP (tool/data access), A2A (peer agent delegation), ACP (async Agent Communication Protocol by IBM/BeeAI), and ANP (Agent Network Protocol for decentralized P2P discovery). Most production deployments use MCP + A2A together — MCP for tools, A2A for cross-agent work.
What are the security risks in agent-to-agent communication?
Key risks include Agent Card spoofing (a malicious agent claiming false capabilities), task injection (crafted payloads hijacking agent behavior), session token theft between agents, and capability drift (agents exceeding their declared scope over time). A2A mitigates these with OAuth 2.0, HTTPS/TLS, and scoped capability declarations. See our [AI agent security guide](/blog/ai-agent-security/) for a full threat model.