NewsAgent

http://localhost:9007/.well-known/agent.json http://localhost:9007/.well-known/agent-card.json

EventInfo Agent

http://localhost:9008/.well-known/agent.json http://localhost:9008/.well-known/agent-card.json

AWS Strands A2A Server

1. http://localhost:9006/docs (with FastAPI)

Start the A2A Server Code

drwxr-xr-x@ 5 welcome  staff     160 Dec 20 23:14 helloworld
(a2a-examples) welcome@jaisairams-Laptop A2A_Examples % python helloworld/__main__.py 
INFO:     Started server process [31227]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:9999 (Press CTRL+C to quit)
INFO:     127.0.0.1:49698 - "GET /.well-known/agent-card.json HTTP/1.1" 200 OK
HTTP GET for authenticated extended card has been called by a client. This endpoint is deprecated in favor of agent/authenticatedExtendedCard JSON-RPC method and will be removed in a future release.
INFO:     127.0.0.1:49698 - "GET /agent/authenticatedExtendedCard HTTP/1.1" 200 OK
INFO:     127.0.0.1:49698 - "POST / HTTP/1.1" 200 OK
INFO:     127.0.0.1:49698 - "POST / HTTP/1.1" 200 OK

test Client example

welcome@jaisairams-Laptop A2A_Examples % source ~/.zprofile.sh
welcome@jaisairams-Laptop A2A_Examples % source .venv/bin/activate
(a2a-examples) welcome@jaisairams-Laptop A2A_Examples % 
(a2a-examples) welcome@jaisairams-Laptop A2A_Examples % python helloworld/test_client.py 
INFO:__main__:Attempting to fetch public agent card from: http://localhost:9999/.well-known/agent-card.json
INFO:httpx:HTTP Request: GET http://localhost:9999/.well-known/agent-card.json "HTTP/1.1 200 OK"
INFO:a2a.client.card_resolver:Successfully fetched agent card data from http://localhost:9999/.well-known/agent-card.json: {'capabilities': {'streaming': True}, 'defaultInputModes': ['text'], 'defaultOutputModes': ['text'], 'description': 'Just a hello world agent', 'name': 'Hello World Agent', 'preferredTransport': 'JSONRPC', 'protocolVersion': '0.3.0', 'skills': [{'description': 'just returns hello world', 'examples': ['hi', 'hello world'], 'id': 'hello_world', 'name': 'Returns hello world', 'tags': ['hello world']}], 'supportsAuthenticatedExtendedCard': True, 'url': 'http://localhost:9999/', 'version': '1.0.0'}
INFO:__main__:Successfully fetched public agent card:
INFO:__main__:{
  "capabilities": {
    "streaming": true
  },
  "defaultInputModes": [
    "text"
  ],
  "defaultOutputModes": [
    "text"
  ],
  "description": "Just a hello world agent",
  "name": "Hello World Agent",
  "preferredTransport": "JSONRPC",
  "protocolVersion": "0.3.0",
  "skills": [
    {
      "description": "just returns hello world",
      "examples": [
        "hi",
        "hello world"
      ],
      "id": "hello_world",
      "name": "Returns hello world",
      "tags": [
        "hello world"
      ]
    }
  ],
  "supportsAuthenticatedExtendedCard": true,
  "url": "http://localhost:9999/",
  "version": "1.0.0"
}
INFO:__main__:
Using PUBLIC agent card for client initialization (default).
INFO:__main__:
Public card supports authenticated extended card. Attempting to fetch from: http://localhost:9999/agent/authenticatedExtendedCard
INFO:httpx:HTTP Request: GET http://localhost:9999/agent/authenticatedExtendedCard "HTTP/1.1 200 OK"
INFO:a2a.client.card_resolver:Successfully fetched agent card data from http://localhost:9999/agent/authenticatedExtendedCard: {'capabilities': {'streaming': True}, 'defaultInputModes': ['text'], 'defaultOutputModes': ['text'], 'description': 'The full-featured hello world agent for authenticated users.', 'name': 'Hello World Agent - Extended Edition', 'preferredTransport': 'JSONRPC', 'protocolVersion': '0.3.0', 'skills': [{'description': 'just returns hello world', 'examples': ['hi', 'hello world'], 'id': 'hello_world', 'name': 'Returns hello world', 'tags': ['hello world']}, {'description': 'A more enthusiastic greeting, only for authenticated users.', 'examples': ['super hi', 'give me a super hello'], 'id': 'super_hello_world', 'name': 'Returns a SUPER Hello World', 'tags': ['hello world', 'super', 'extended']}], 'supportsAuthenticatedExtendedCard': True, 'url': 'http://localhost:9999/', 'version': '1.0.1'}
INFO:__main__:Successfully fetched authenticated extended agent card:
INFO:__main__:{
  "capabilities": {
    "streaming": true
  },
  "defaultInputModes": [
    "text"
  ],
  "defaultOutputModes": [
    "text"
  ],
  "description": "The full-featured hello world agent for authenticated users.",
  "name": "Hello World Agent - Extended Edition",
  "preferredTransport": "JSONRPC",
  "protocolVersion": "0.3.0",
  "skills": [
    {
      "description": "just returns hello world",
      "examples": [
        "hi",
        "hello world"
      ],
      "id": "hello_world",
      "name": "Returns hello world",
      "tags": [
        "hello world"
      ]
    },
    {
      "description": "A more enthusiastic greeting, only for authenticated users.",
      "examples": [
        "super hi",
        "give me a super hello"
      ],
      "id": "super_hello_world",
      "name": "Returns a SUPER Hello World",
      "tags": [
        "hello world",
        "super",
        "extended"
      ]
    }
  ],
  "supportsAuthenticatedExtendedCard": true,
  "url": "http://localhost:9999/",
  "version": "1.0.1"
}
INFO:__main__:
Using AUTHENTICATED EXTENDED agent card for client initialization.
/Users/welcome/Desktop/Tech_Repos/python_envs/A2A/A2A_event_agents/A2A_Examples/helloworld/test_client.py:105: DeprecationWarning: A2AClient is deprecated and will be removed in a future version. Use ClientFactory to create a client with a JSON-RPC transport.
  client = A2AClient(
INFO:__main__:A2AClient initialized.
INFO:httpx:HTTP Request: POST http://localhost:9999/ "HTTP/1.1 200 OK"
{'id': '69c93f2c-130e-4fea-a02c-c32bcc1c8b04', 'jsonrpc': '2.0', 'result': {'kind': 'message', 'messageId': 'bab14d85-8168-4c39-bf10-e31671358dd2', 'parts': [{'kind': 'text', 'text': 'Hello World'}], 'role': 'agent'}}
INFO:httpx:HTTP Request: POST http://localhost:9999/ "HTTP/1.1 200 OK"
{'id': 'b4cae74c-1b7c-49fd-9b27-d152a80015f8', 'jsonrpc': '2.0', 'result': {'kind': 'message', 'messageId': '33420605-7151-41d0-917c-1eff0dde2c86', 'parts': [{'kind': 'text', 'text': 'Hello World'}], 'role': 'agent'}}
(a2a-examples) welcome@jaisairams-Laptop A2A_Examples % 

Interactive Batch and Streaming messages

# 6. Interacting with the Server

With the Helloworld A2A server running, let's send some requests to it. The SDK includes a client (`A2AClient`) that simplifies these interactions.

## The Helloworld Test Client

The `test_client.py` script demonstrates how to:

1. Fetch the Agent Card from the server.
2. Create an `A2AClient` instance.
3. Send both non-streaming (`message/send`) and streaming (`message/stream`) requests.

Open a **new terminal window**, activate your virtual environment, and navigate to the `a2a-samples` directory.

Activate virtual environment (Be sure to do this in the same directory where you created the virtual environment):

=== "Mac/Linux"

    ```sh
    source .venv/bin/activate
    ```

=== "Windows"

    ```powershell
    .venv\Scripts\activate
    ```

Run the test client:

```bash
# from the a2a-samples directory
python samples/python/agents/helloworld/test_client.py

Understanding the Client Code

Let's look at key parts of test_client.py:

1. Fetching the Agent Card & Initializing the Client:

   --8<-- "https://raw.githubusercontent.com/a2aproject/a2a-samples/refs/heads/main/samples/python/agents/helloworld/test_client.py:A2ACardResolver"

   The A2ACardResolver class is a convenience. It first fetches the AgentCard from the server's /.well-known/agent-card.json endpoint (based on the provided base URL) and then initializes the client with it.

2. Sending a Non-Streaming Message (send_message):

   --8<-- "https://raw.githubusercontent.com/a2aproject/a2a-samples/refs/heads/main/samples/python/agents/helloworld/test_client.py:send_message"

   • The send_message_payload constructs the data for MessageSendParams.
   • This is wrapped in a SendMessageRequest.
   • It includes a message object with the role set to "user" and the content in parts.
   • The Helloworld agent's execute method will enqueue a single "Hello World" message. The DefaultRequestHandler will retrieve this and send it as the response.
   • The response will be a SendMessageResponse object, which contains either a SendMessageSuccessResponse (with the agent's Message as the result) or a JSONRPCErrorResponse.

3. Handling Task IDs (Illustrative Note for Helloworld):

   The Helloworld client (test_client.py) doesn't attempt get_task or cancel_task directly because the simple Helloworld agent's execute method, when called via message/send, results in the DefaultRequestHandler returning a direct Message response rather than a Task object. More complex agents that explicitly manage tasks (like the LangGraph example) would return a Task object from message/send, and its id could then be used for get_task or cancel_task.

4. Sending a Streaming Message (send_message_streaming):

   --8<-- "https://raw.githubusercontent.com/a2aproject/a2a-samples/refs/heads/main/samples/python/agents/helloworld/test_client.py:send_message_streaming"

   • This method calls the agent's message/stream endpoint. The DefaultRequestHandler will invoke the HelloWorldAgentExecutor.execute method.
   • The execute method enqueues one "Hello World" message, and then the event queue is closed.
   • The client will receive this single message as one SendStreamingMessageResponse event, and then the stream will terminate.
   • The stream_response is an AsyncGenerator.

Expected Output

When you run test_client.py, you'll see JSON outputs for:

• The non-streaming response (a single "Hello World" message).
• The streaming response (a single "Hello World" message as one chunk, after which the stream ends).

The id fields in the output will vary with each run.

// Non-streaming response
{"jsonrpc":"2.0","id":"xxxxxxxx","result":{"type":"message","role":"agent","parts":[{"type":"text","text":"Hello World"}],"messageId":"yyyyyyyy"}}
// Streaming response (one chunk)
{"jsonrpc":"2.0","id":"zzzzzzzz","result":{"type":"message","role":"agent","parts":[{"type":"text","text":"Hello World"}],"messageId":"wwwwwwww","final":true}}

(Actual IDs like xxxxxxxx, yyyyyyyy, zzzzzzzz, wwwwwwww will be different UUIDs/request IDs)

This confirms your server is correctly handling basic A2A interactions with the updated SDK structure!

Now you can shut down the server by typing Ctrl+C in the terminal window where __main__.py is running.

# Langgraph