A2A (Agent-to-Agent Protocol)

A2A is an open protocol for agents to talk to other agents: discover each other, delegate tasks, report progress. MCP connects an agent to tools. A2A connects agents to agents.

First question: do you actually need it? A2A solves coordination between agents owned by different teams or vendors. If all your agents live in one codebase, function calls and subagents are simpler. Every agent hop adds latency, cost, and a failure mode.

MCP vs A2A

Aspect	MCP	A2A
Purpose	Agent ↔ tools and data	Agent ↔ agent
Originated at	Anthropic	Google (now Linux Foundation)
Use case	Database queries, API calls	Multi-agent collaboration
Direction	Agent calls external systems	Agents delegate and negotiate

Architecture

Key capabilities

Discovery: find agents by capability through published agent cards
Delegation: hand subtasks to specialist agents
Negotiation: agree on formats and constraints
Status updates: long-running tasks report progress
Cross-organization: agents from different teams or vendors work together

When to use

Use MCP	Use A2A
Query a database	Delegate research to another team's agent
Call an API	Coordinate a workflow across independently owned agents
Read and write files	Get a review from another org's review agent
Run commands	Fan work out across agents you don't control

A2A + MCP together

Systems that need A2A usually use both:

User → Orchestrator Agent (A2A) → Specialist Agents (A2A)
                                       ↓
                                  MCP Servers → External Systems

Treat agent links like service APIs: versioned capabilities, authentication, timeouts, defined failure behavior, and end-to-end tracing. Multi-agent failures are distributed-systems failures, and you debug them the same way.

Example prompts:

Multi-agent workflow:
"Design a system where a planning agent splits work, coding agents implement in
parallel, and a review agent validates. A2A between agents, MCP for tool access.
Include timeouts and failure handling."

Cross-team:
"Our coding agent requests deploys from the platform team's deploy agent.
Design the A2A flow: authentication, status callbacks, and what happens on timeout."

Reference: https://a2a-protocol.org/