A2A JSON-RPC

Communicate with an assistant using the Agent-to-Agent (A2A) Protocol over JSON-RPC 2.0. This endpoint accepts a JSON-RPC envelope and dispatches based on method.

Supported Methods:

• message/send: Send a message and wait for the final Task result.
• message/stream: Send a message and receive Server-Sent Events (SSE) JSON-RPC responses.
• tasks/get: Fetch the current state of a Task by ID.
• tasks/cancel: Request cancellation (currently not supported; returns an error).

LangGraph Mapping:

• message.contextId maps to LangGraph thread_id.

Notes:

• Only text and data parts are supported; file parts are not.
• If message.contextId is omitted, a new context is created.
• Text parts require the assistant input schema to include a messages field.

POST /a2a/{assistant_id}

cURL

message_send

curl --request POST \
  --url https://api.example.com/a2a/{assistant_id} \
  --header 'Accept: <accept>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "message/send",
  "params": {
    "message": {
      "role": "user",
      "parts": [
        {
          "kind": "text",
          "text": "Hello from A2A"
        },
        {
          "kind": "data",
          "data": {
            "locale": "en-US"
          }
        }
      ],
      "messageId": "msg-1",
      "contextId": "f5bd2a40-74b6-4f7a-b649-ea3f09890003"
    }
  }
}
'

200

task_result

{
  "jsonrpc": "2.0",
  "id": "1",
  "result": {
    "kind": "task",
    "id": "run-uuid",
    "contextId": "f5bd2a40-74b6-4f7a-b649-ea3f09890003",
    "status": {
      "state": "completed"
    },
    "artifacts": [
      {
        "artifactId": "artifact-uuid",
        "name": "Assistant Response",
        "parts": [
          {
            "kind": "text",
            "text": "Hello back"
          }
        ]
      }
    ]
  }
}

Headers

Accept · string · required

For message/stream, must include text/event-stream. For all other methods, use application/json.

Path Parameters

assistant_id · string<uuid> · required

The ID of the assistant to communicate with

Body

application/json

jsonrpc · enum<string> · required

JSON-RPC version

Available options: 2.0

id · string · required

Request identifier

method · enum<string> · required

The method to invoke

Available options: message/send, message/stream, tasks/get, tasks/cancel

params · Message Send/Stream Parameters · object

Method parameters; shape depends on the method.

Message Send/Stream Parameters

Task Get Parameters

Task Cancel Parameters

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Response

200

application/json

JSON-RPC response for non-streaming methods. For message/stream, the response is an SSE stream of JSON-RPC envelopes.

jsonrpc · enum<string> · required

Available options: 2.0

id · string · required

result · object

Success result containing task information or task details

error · object

Error information if request failed

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