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

Show child attributes

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

Show child attributes