A2Aで大事なのは「Agent同士をつなぐこと」ではなく「他のAgentに仕事を安全に委任できること」 A2Aで大事なのは「Agent同士をつなぐこと」ではなく「他のAgentに仕事を安全に委任できること」

When people first encounter A2A, or the Agent2Agent Protocol, they tend to describe it as a way to "connect agents to each other," as if the headline feature were a kind of chat channel between autonomous systems. The more important framing, and the one that explains why the protocol exists at all, is that A2A is about being able to delegate work to another agent safely, especially when that other agent runs on a different vendor's stack, a different framework, or inside a different organization entirely. The connection is the easy part; the trust and accountability around the delegation is the hard part, and it is where the design effort goes.

A2A was introduced by Google in 2025 as an open protocol and later moved under the stewardship of the Linux Foundation, with backing from a range of companies building agentic systems. It is frequently positioned as complementary to the Model Context Protocol, or MCP, which Anthropic introduced to standardize how a model or agent reaches out to tools and data sources. A common way to summarize the split is that MCP connects an agent to its tools, while A2A connects an agent to other agents. In practice the two are likely to be used together: an agent might use MCP to call a database or an API, and use A2A to hand off a sub-task to a specialized peer agent that it does not control.

The technical building blocks reflect this delegation-first mindset. A2A defines the notion of an Agent Card, a machine-readable description, typically served as JSON at a well-known endpoint, that advertises what an agent can do, how to reach it, and what authentication it expects. A client agent discovers a remote agent through this card, then opens a task, which is the unit of delegated work. Communication is built on familiar web foundations such as HTTP and JSON-RPC, with support for streaming updates through server-sent events so that long-running tasks can report progress, and for asynchronous patterns where a task may take minutes or hours to complete. Results come back as structured messages and artifacts rather than as a freeform chat transcript, which makes the outcome of a delegation easier to consume programmatically.

Why does the "safe" qualifier matter so much? Once an agent can ask another agent to act on its behalf, several questions immediately follow that do not arise in a simple tool call. Who is the requesting party, and can the receiving agent verify that identity? What is the scope of the authority being granted, and how do you prevent an over-broad request from triggering actions the caller never intended? How is the work audited after the fact, so an organization can reconstruct what was delegated to whom and what was done in response? These are the same governance concerns that enterprises apply to human contractors and to service-to-service API calls, and they become more acute when the actor on the other side is a non-deterministic agent that may interpret instructions loosely. A2A leans on established mechanisms such as standard authentication schemes and explicit capability declarations rather than inventing new security primitives, which appears to be a deliberate choice to fit into existing enterprise controls.

This framing also clarifies what A2A is not. It is not primarily a way to make agents converse for its own sake, and it does not by itself solve the harder problems of agent reliability, prompt injection, or accountability when a delegated task goes wrong. Those remain open challenges across the industry, and any protocol can only provide the scaffolding for trust, not guarantee good behavior. The protocol's value is in offering a vendor-neutral contract so that an agent built with one framework can request work from an agent built with another without bespoke integration each time.

For teams evaluating where this fits, the practical takeaway is to treat A2A as an interoperability and delegation layer rather than a feature checkbox. The questions worth asking are whether the agents you depend on can be described, discovered, authenticated, and audited, not merely whether they can talk. As multi-agent systems spread across organizational boundaries, the ability to delegate a task to an unfamiliar agent and still retain confidence in identity, scope, and traceability is likely to be the differentiator, and that is the part of A2A worth focusing on.