What Is the A2A Protocol? | GEO Glossary

The A2A (Agent2Agent) protocol is an open standard that lets AI agents built by different vendors on different frameworks discover each other, communicate securely, and hand off work. Google announced it in April 2025 with 50+ partners and donated it to the Linux Foundation that June, where it is now maintained under neutral governance with an Apache 2.0 license.

Why It Matters

As the agent ecosystem grows, the structure shifts from "one agent does everything" to "specialist agents collaborate." The problem: each agent is built by a different company on a different platform. A2A acts as the common language between them. Where MCP connects agents to tools and data, A2A connects agents to agents — together they form the communication stack of the agentic web. A v1.0 stable release arrived in 2026; by April of that year more than 150 organizations were involved, with GA support in major platforms like Microsoft Copilot Studio, Azure AI Foundry, and Amazon Bedrock AgentCore — production use, not pilots.

How It Works

A2A builds on existing web standards: HTTP, SSE, and JSON-RPC.

Agent Card: A JSON document in which an agent declares its identity and capabilities. Published at a standard address, it lets other agents decide what work can be delegated. Recent versions add signatures for domain verification.
Task lifecycle: Collaboration happens in units of Tasks, with state tracking and streaming for everything from instant requests to long-running jobs that take hours.
Design principles: Secure by default (enterprise-grade authN/authZ), support for long-running tasks, and modality agnosticism spanning text, audio, and video.

Relationship with MCP

A2A and MCP are complements, not competitors. MCP standardizes the "vertical" connection — an agent calling tools and fetching context, much like function calling — while A2A standardizes the "horizontal" connection of agents delegating work to each other. Real multi-agent systems use both: each agent drives its own tools via MCP and collaborates with other agents via A2A. Extensions like AP2 (Agent Payments Protocol), which handles payments, are being layered onto the same stack.

GEO Implications

As A2A spreads, "via agents" becomes a new path through which content and services get discovered. A user's personal agent delegates to a travel-booking agent, which then chooses which information sources to consult. To be chosen in that environment, content must be machine-readable and brand information must stay consistent across the agent ecosystem. Content teams will rarely implement A2A directly, but the direction it signals — agent-mediated discovery as the next stage of search — feeds straight into content strategy.

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How inblog Helps

As agent-to-agent collaboration grows, content is increasingly read by agents before people. The structured markup and clear metadata of an inblog blog give agents the evidence they need to judge a piece's topic and trustworthiness. Formats agents can excerpt easily — comparison tables, FAQs, crisp definition paragraphs — raise the odds your content gets picked even in multi-agent environments.