a2a docs›reference›mcp http

a2a_pack.mcp.http

Streamable HTTP transport for MCP (with elicitation support).

Exposes POST /mcp for client→server requests. When a tool call drives the skill into ctx.collect / ctx.ask, the server pushes elicitation/create requests back to the client interleaved on the SSE response, and routes the client's responses (delivered via a follow-up POST /mcp on the same Mcp-Session-Id) to the in-flight future.

Content negotiation:

  • Accept: application/json (or no Accept) — one-shot JSON response. Skills that call ctx.collect/ctx.ask over this path will time out, because there is no channel to deliver the request to the client.
  • Accept includes text/event-stream — SSE response. Elicitation works end-to-end.

Mountable into an existing FastAPI app via :func:mount_http, or serveable standalone via :func:build_http_app.

ElicitError (class)

Raised when the client declines/cancels an elicitation request or returns a JSON-RPC error in response to one.

build_http_app (function)

build_http_app(agent: 'A2AAgent') -> 'FastAPI'

Build a minimal FastAPI app exposing only the MCP endpoint.

mount_http (function)

mount_http(app: 'FastAPI', agent: 'A2AAgent', *, prefix: 'str' = '/mcp') -> 'None'

Mount the MCP endpoint onto an existing FastAPI app.

Source: apps/a2a/a2a_pack/mcp/http.py