> For the complete documentation index, see [llms.txt](https://docs.orbitfin.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.orbitfin.ai/orbit-api-reference/a2a/1.-what-is-a2a.md).

# 1. What is A2A?

**A2A (Agent2Agent)** is an open industry-standard protocol that enables AI agents built by different vendors and on different platforms to discover, communicate, and collaborate with one another. You can think of A2A as a standardized way for one agent to use another agent as a callable "capability"—without having to write custom integration code for the other party in advance.

\
Core Concepts

**Limitations of traditional agent integration:**

* Every agent platform has its own proprietary interface, and they cannot directly call one another
* To make Platform A call an agent on Platform B, you have to build a dedicated set of custom integration code
* There is no unified "capability discovery" mechanism between agents, requiring manual alignment of documentation before onboarding
* Every time you add a new partner platform, you have to develop the integration logic all over again

**Capabilities enabled by A2A:**

* **Standardized discovery (Agent Card):** An agent can publish a "business card" that declares its name, capabilities, and authentication methods, which other agents can read automatically
* **Any agent is callable:** As long as both sides support A2A, no dedicated integration code needs to be developed in advance
* **Stateful multi-turn collaboration:** Both the caller and the callee can maintain their own multi-turn task context, rather than being limited to a one-off function call
* **Built-in authentication and security:** Standard identity authentication methods are defined at the protocol level, so there's no need to design a separate authorization mechanism

### How A2A Works <a href="#heading-8c53bcd6-01f5-4af4-8fa5-ecfb75200503--how-a2a-works-0" id="heading-8c53bcd6-01f5-4af4-8fa5-ecfb75200503--how-a2a-works-0"></a>

When an agent (whether one you built yourself or a platform like Microsoft Copilot Studio) needs to use the capabilities of Agent Builder, A2A completes a collaboration roughly through the following steps:

1. **Discover:** Read Agent Builder's Agent Card to learn its name, feature descriptions, and available capabilities
2. **Decide:** Based on the user's request, the caller independently determines whether this interaction requires Agent Builder
3. **Call:** When needed, initiate the call via a standard JSON-RPC request, carrying identity credentials
4. **Respond:** Agent Builder processes the request and returns the result, and the caller decides how to present it to the end user
5. **Continue:** Subsequent requests carry the same context identifier, allowing the same conversation/task to continue

### Difference from MCP <a href="#heading-8c53bcd6-01f5-4af4-8fa5-ecfb75200503--difference-from-mcp-0" id="heading-8c53bcd6-01f5-4af4-8fa5-ecfb75200503--difference-from-mcp-0"></a>

MCP (Model Context Protocol) addresses "how a model/agent calls tools and accesses data sources"; A2A addresses "how one agent calls another agent," where both sides can have their own reasoning capabilities and maintain their own multi-turn task state, rather than being limited to a one-way function call.