# Agent2Agent protocol (A2A)

Category: [Agents & Protocols](https://seo-geo-glossary.com/en/glossary/category/agents-protocols/) › [Agent protocols](https://seo-geo-glossary.com/en/glossary/category/agents-protocols/agent-protocols/) · Also known as: A2A

The **Agent2Agent protocol (A2A)** is an open protocol that lets AI agents built on different frameworks and by different vendors communicate and coordinate work. Google announced it on April 9, 2025. The project is hosted under the Linux Foundation and licensed under Apache 2.0. On August 27, 2026, it announced that it is joining the Agentic AI Foundation. The current specification is version 1.0, most recently published as release v1.0.1 of May 28, 2026 (as of October 2026).

## How does A2A work?

A client agent hands a task to a remote agent, which carries it out and returns a result. To find a suitable remote agent, the client reads its **Agent Card**, a JSON document that describes what the agent can do and how to connect to it.

Work runs through **tasks** with a defined lifecycle. Messages use JSON-RPC 2.0 over HTTP(S). For long-running tasks, A2A supports streaming with Server-Sent Events and asynchronous notifications. Agents do not have to expose their internal logic, tools or memory, they exchange messages and results. Authentication can use schemes such as API keys, OAuth 2.0 or OpenID Connect, as IBM summarizes.

SDKs exist for Python, Go, JavaScript, Java, .NET and Rust.

## A2A and MCP

The A2A project positions the two protocols as complementary. MCP connects an AI application to tools and data. A2A connects agents with each other. IBM gives an example: an inventory agent checks stock through MCP and then notifies an order agent through A2A.

## Example

A purchasing agent needs office supplies. It reads the Agent Card of a supplier's agent and sees which requests the agent accepts. It sends a task with the order, follows status updates and receives the confirmation as the task result.

## Common mistakes

- **Building from version 0.3 examples.** Appendix A of the specification lists changes for version 1.0, including the removal of the Kind Discriminator. Code and Agent Cards written from older examples may not match clients that expect 1.0.
- **Setting the extended Agent Card flag in the old place.** The former top-level field `supportsExtendedAgentCard` moved to `capabilities.extendedAgentCard`. The specification recommends that clients check both locations during the migration.

## FAQ

**What does A2A stand for?**
Agent2Agent, meaning communication from one agent to another.

**Who governs A2A?**
It is an open source project under the Linux Foundation, contributed by Google.

**How does A2A differ from MCP?**
MCP gives a model access to tools and data. A2A lets agents delegate work to other agents.

## At a glance

- **Publisher:** Google (announced 2025-04-09), project at the Linux Foundation
- **Connects:** AI agents from different vendors with each other
- **Status:** specification 1.0, release v1.0.1 (2026-05-28)
- **License:** Apache 2.0
- **Specification:** [A2A Protocol Specification](https://a2a-protocol.org/latest/specification/)

Last checked: October 8, 2026

## AI agent protocols compared

| Protocol | Publisher | Connects | Status and version |
|---|---|---|---|
| MCP (Model Context Protocol) | by Anthropic, since 2025-12-09 at the Agentic AI Foundation (Linux Foundation) | AI applications with servers that provide data, tools and prompts | current version 2026-07-28 |
| A2A (Agent2Agent) | by Google, donated to the Linux Foundation; joining the Agentic AI Foundation announced on 2026-08-27 | AI agents from different vendors with each other | specification 1.0 (release v1.0.1 of 2026-05-28) |
| ACP (Agentic Commerce Protocol) | OpenAI and Stripe | buyers and their AI agents with businesses and payment providers | beta, current version 2026-04-17 |
| AP2 (Agent Payments Protocol) | Google; standardisation continues in FIDO Alliance working groups | AI agents, merchants and payment providers for payments on behalf of users | v0.2 (release of 2026-04-28) |
| UCP (Universal Commerce Protocol) | Google with commerce partners (incl. Shopify, Etsy, Wayfair, Target, Walmart) | platforms and AI agents with businesses (profile at /.well-known/ucp) | stable, version 2026-08-25 |
| WebMCP | W3C Web Machine Learning Community Group (editors from Microsoft and Google) | websites with AI agents in the browser | draft (Draft Community Group Report of 2026-10-02), not a W3C standard; origin trial in Chrome from version 149 |
| NLWeb | Microsoft (announced 2025-05-19), open source under the MIT licence | websites (Schema.org and RSS content) with users and AI agents; every instance is an MCP server | open-source project without a published version number |

Sources: [Model Context Protocol: Specification 2026-07-28](https://modelcontextprotocol.io/specification/2026-07-28); [Model Context Protocol: Versioning](https://modelcontextprotocol.io/specification/versioning); [Anthropic: Donating the Model Context Protocol and establishing the Agentic AI Foundation (2025-12-09)](https://www.anthropic.com/news/donating-the-model-context-protocol-and-establishing-of-the-agentic-ai-foundation); [A2A Protocol: Specification](https://a2a-protocol.org/latest/specification/); [A2A: A new chapter for A2A, joining the Agentic AI Foundation (2026-08-27)](https://a2a-protocol.org/latest/blog/2026/08/27/a-new-chapter-for-a2a-joining-the-agentic-ai-foundation/); [A2A releases (GitHub)](https://github.com/a2aproject/A2A/releases); [Agentic Commerce Protocol (GitHub)](https://github.com/agentic-commerce-protocol/agentic-commerce-protocol); [AP2: Agent Payments Protocol](https://ap2-protocol.org/); [AP2 releases (GitHub)](https://github.com/google-agentic-commerce/AP2/releases); [Universal Commerce Protocol: Specification overview (2026-08-25)](https://ucp.dev/latest/specification/overview/); [Universal Commerce Protocol](https://ucp.dev/); [WebMCP: Draft Community Group Report (W3C Web Machine Learning CG)](https://webmachinelearning.github.io/webmcp/); [Chrome for Developers: WebMCP (updated 2026-10-07)](https://developer.chrome.com/docs/ai/webmcp); [Microsoft: Introducing NLWeb (2025-05-19)](https://news.microsoft.com/source/features/company-news/introducing-nlweb-bringing-conversational-interfaces-directly-to-the-web/); [NLWeb (GitHub)](https://github.com/nlweb-ai/NLWeb). Last checked: October 8, 2026

*Diagram: Which protocol covers what?.* Map of agent protocols as of 2026-10-08: which connection each protocol covers, who publishes it and what its status is. In commerce, ACP, UCP and AP2 overlap, and several protocols build on MCP or A2A. Versions change quickly.

## Not to be confused with

- [MCP (Model Context Protocol)](https://seo-geo-glossary.com/en/glossary/mcp/index.md): connects an AI application to servers that provide tools, data and prompts. According to the A2A project, the two protocols complement each other.

## Related terms

- [MCP (Model Context Protocol)](https://seo-geo-glossary.com/en/glossary/mcp/index.md)
- [Agentic Commerce Protocol (ACP)](https://seo-geo-glossary.com/en/glossary/agentic-commerce-protocol/index.md)
- [Agent Payments Protocol (AP2)](https://seo-geo-glossary.com/en/glossary/agent-payments-protocol/index.md)
- [Universal Commerce Protocol (UCP)](https://seo-geo-glossary.com/en/glossary/universal-commerce-protocol/index.md)
- [AI agent](https://seo-geo-glossary.com/en/glossary/ai-agent/index.md)

## Sources

- [A2A: A new era of agent interoperability – Google Developers Blog (Apr 9, 2025)](https://developers.googleblog.com/en/a2a-a-new-era-of-agent-interoperability/)
- [Agent2Agent (A2A) – GitHub a2aproject/a2a](https://github.com/a2aproject/a2a)
- [Linux Foundation Launches the Agent2Agent Protocol Project](https://www.linuxfoundation.org/press/linux-foundation-launches-the-agent2agent-protocol-project-to-enable-secure-intelligent-communication-between-ai-agents)
- [What is Agent2Agent protocol? – IBM (secondary)](https://www.ibm.com/think/topics/agent2agent-protocol)
- [A2A Protocol Specification – a2a-protocol.org](https://a2a-protocol.org/latest/specification/)
- [A2A: A new chapter for A2A, joining the Agentic AI Foundation (2026-08-27)](https://a2a-protocol.org/latest/blog/2026/08/27/a-new-chapter-for-a2a-joining-the-agentic-ai-foundation/)
- [A2A releases – GitHub](https://github.com/a2aproject/A2A/releases)

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Last updated: October 8, 2026
URL: https://seo-geo-glossary.com/en/glossary/agent2agent-protocol/