Agent to Agent Protocol (A2A)

How do AI agents talk to each other?

Agent to Agent Protocol (A2A) from Google provides structured communication flows for autonomous systems to coordinate, delegate tasks, and collaborate without human intermediaries.

The Protocol Stack

A2A is the communication layer. Google extended it with AP2 (Agent Payments Protocol) for agent-led payments, and x402 with Coinbase for crypto-native agent transactions.

Layer	Protocol	Function	Analogy
Communication	A2A	Agent-to-agent coordination	TCP
Tools	MCP	Agent-to-tool access	HTTP
Payment	AP2 / x402 / ACP	Agent-to-payment	SMTP

Launched with 50+ partners including Atlassian, PayPal, Salesforce. AP2 added 60+ more including Mastercard, AmEx, Coinbase.

Links

• A2A GitHub
• A2A vs MCP
• Google AP2 Announcement
• A2A x402 Extension

Context

• Agent Commerce — The standards war for agent transactions
• MCP — Model Context Protocol for tool use
• Payment Rails — Intent-based payment infrastructure
• Standards — What protocols become when adopted
• Protocols — Rules for making progress