a2a #

This package provides an SDK for the Agent 2 Agent(A2A) protocol which provides an open protocol enabling communication and interoperability between opaque agentic applications. Please see here for the A2A project overview. This package assumes some familiarity with the A2A project in terms of goals, terminology etc.

Specifically the project implements an A2A SDK for Dart, modelled from the JavaScript SDK that can be found here.

The roadmap for the package is that the initial release contains the A2AClient, to be followed by implementation of the cli-client, the server functionality and a sample agent.

The SDK consists of the following components :-

The A2A Client #

The A2A client(A2AClient) provides the client API for an agent. This allows users to send messages, streaming messages using SSE responses, fetching of an agents agent card and other management functions such as agent configuration and task resubscription.

Key Features :-

• JSON-RPC Communication: Handles sending requests and receiving responses (both standard and streaming via Server-Sent Events) according to the JSON-RPC 2.0 specification.

• A2A Methods: Implements standard A2A methods like sendMessage, sendMessageStream, getTask, cancelTask, setTaskPushNotificationConfig, getTaskPushNotificationConfig, and resubscribeTask.

• Error Handling: Provides basic error handling for network issues and JSON-RPC errors.

• Streaming Support: Manages Server-Sent Events (SSE) for real-time task updates (sendMessageStream, resubscribeTask).

Annotated examples of use for the A2AClient to communicate with a test agent can be found in the examples directory, here.

The A2A CLI Client #

The A2A CLI client(a2a_cli_client) provides a simple CLI client for interacting with an agent. The client supports fetching and display of an agents agent card, querying of an agent using normal send message or streaming requests if streaming is supported.

Responses are handled and displayed to the user to allow visibility of the request/response interplay between the client and the agent for a particular request.

The client supports the following commands that can be entered at the prompt :-

• /exit - exits the client.
• /new - starts a new session by clearing any current task and context information.
• /resub - attempts to resubscribe an already started task if the SSE event stream for a previous task has been broken.

THh client is installed in the usual manner i.e.

dart pub global activate a2a

This will give you command line access to the a2a_cli_client.

The A2A Server #

Not yet implemented - will be in a subsequent version

Sample agent #

Not yet implemented - will be in a subsequent version

Several sample agents implemented in various languages can be found here