What is the primary distinction between MCP and Google's A2A protocol?

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Quick reference

TL;DR

MCP connects an agent to tools and data; A2A connects an agent to other agents. Different layers, complementary, not competing.

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Easy to grasp

Picture a worker at a desk. MCP is the worker reaching for tools on the desk: a calculator, a filing cabinet, a printer. It is how one worker grabs and uses equipment. A2A is two workers talking across the office to split a job: 'You handle the invoices, I'll draft the report, send me yours when done.' One protocol is about a single agent picking up tools. The other is about agents coordinating and delegating work to peers. They never fight over the same job. A real system uses both at once: each agent uses MCP to touch its own tools, and the agents use A2A to hand tasks back and forth.

Key concepts

Agent-to-Agent protocol AI agents Multi-agent orchestration

Quick scan · 2–4 min

Everything important, quickly.

3 min: two-axis framing (vertical MCP vs horizontal A2A) + what each boundary crosses + both open + one stack that uses both together.

Side-by-side

Concern	MCP	A2A
Boundary	Agent to tools and data	Agent to peer agent
Core question	How does an agent access capabilities?	How do agents delegate and coordinate?
Unit of interaction	Tool call, resource read, prompt	Task with messages and artifacts
Discovery	tools/list, resources/list	Agent Card at well-known URL
Openness	Open spec, Anthropic origin	Open spec, Google origin
Relationship	Complementary, lower layer	Complementary, peer layer

Real-world examples

Real products, models, and research that use this idea.

Google introduced A2A in 2025 with partners, positioning it as complementary to Anthropic's MCP rather than a replacement.
An orchestrator agent delegates a research subtask to a specialist agent via A2A, and that specialist queries Postgres through an MCP server.
A2A's Agent Card published at a well-known URL lets one agent discover another's skills, much as MCP's tools/list discovers tool catalogs.

Interviewer follow-ups

What an interviewer would ask next. Try answering before peeking at the approach.

QWalk me through a system where an agent uses both MCP and A2A in a single workflow.

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QWhy is modeling a remote agent as just another MCP tool a poor design choice?

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QWhat does A2A's Agent Card contain, and what is the MCP analogue?

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60-second cheat sheet

The night-before-the-interview bullets. Scan these on the way to the call.

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References

Primary sources. Skim if you want the original framing.