A2A (Agent-to-Agent)¶

agentscope-extensions-a2a implements the A2A protocol and ships two sub-modules:

agentscope-extensions-a2a-client: wraps a remote A2A Agent as a local Agent you can call(...) directly.
agentscope-extensions-a2a-server: exposes a local ReActAgent as an A2A Server.

The two modules are independent — use either one alone.

Client: call a remote A2A Agent¶

Add the dependency¶

<dependency>
    <groupId>io.agentscope</groupId>
    <artifactId>agentscope-extensions-a2a-client</artifactId>
    <version>${agentscope.version}</version>
</dependency>

Pass an AgentCard directly¶

import io.a2a.spec.AgentCard;
import io.agentscope.core.a2a.agent.A2aAgent;

AgentCard card = AgentCard.builder()
    .name("remote-translator")
    .url("http://other-service:8080")
    // ...
    .build();

A2aAgent remote = A2aAgent.builder()
    .name("remote-translator")
    .agentCard(card)
    .build();

Msg result = remote.call(new UserMessage("Translate to English: 你好")).block();

Auto-discover via well-known¶

import io.agentscope.core.a2a.agent.card.WellKnownAgentCardResolver;

WellKnownAgentCardResolver resolver = new WellKnownAgentCardResolver(
    "http://127.0.0.1:8080",
    "/.well-known/agent-card.json",
    Map.of()
);

A2aAgent remote = A2aAgent.builder()
    .name("remote")
    .agentCardResolver(resolver)
    .build();

A2aAgent is a subclass of AgentBase, so it composes naturally with Pipeline, MsgHub, Subagent, etc.

Server: expose a ReActAgent as an A2A Server¶

Add the dependency¶

<dependency>
    <groupId>io.agentscope</groupId>
    <artifactId>agentscope-extensions-a2a-server</artifactId>
    <version>${agentscope.version}</version>
</dependency>

Build the server¶

import io.agentscope.core.a2a.server.AgentScopeA2aServer;
import io.agentscope.core.a2a.server.transport.jsonrpc.JsonRpcTransportProperties;

ReActAgent.Builder agentBuilder = ReActAgent.builder()
    .name("backend-agent")
    .model(model);

AgentScopeA2aServer server = AgentScopeA2aServer.builder()
    .agentBuilder(agentBuilder)
    .transportProperties(new JsonRpcTransportProperties())
    // .agentCard(customCard)
    // .agentRegistry(myRegistry)
    .build();

// Delegate inbound requests to the transport wrapper from your web framework
TransportWrapper wrapper = server.getTransportWrapper("JSONRPC");
// ... Spring/Quarkus controller forwards to wrapper.handle(...)

server.postEndpointReady();   // call after the web server is listening — triggers registration etc.

AgentScopeA2aServer does not bind a port or expose endpoints itself; it only assembles components and the request-handling chain. You wire transport into Spring Boot, Quarkus, Vert.x, etc. as you prefer.

Optional components¶

TaskStore / QueueManager: task and event queue stores; in-memory by default, swap for persistent versions in production.
PushNotificationConfigStore / PushNotificationSender: outbound notifications.
AgentRegistry: register AgentCard to an external registry such as Nacos (see Nacos).

Spring Boot Starter¶

If you’re on Spring Boot, prefer agentscope-spring-boot-starter-a2a-server — it auto-configures the server and controller. See Spring Boot Starters.