refactor: move transport-specific parameters from FastMCP constructor to run() (#1898)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

examples/servers/everything-server/mcp_everything_server/server.py

@@ -83,8 +83,6 @@ event_store = InMemoryEventStore()
 
 mcp = FastMCP(
     name="mcp-conformance-test-server",
-    event_store=event_store,
-    retry_interval=100,  # 100ms retry interval for SSE polling
 )
 
 
@@ -448,8 +446,12 @@ def main(port: int, log_level: str) -> int:
     logger.info(f"Starting MCP Everything Server on port {port}")
     logger.info(f"Endpoint will be: http://localhost:{port}/mcp")
 
-    mcp.settings.port = port
-    mcp.run(transport="streamable-http")
+    mcp.run(
+        transport="streamable-http",
+        port=port,
+        event_store=event_store,
+        retry_interval=100,  # 100ms retry interval for SSE polling
+    )
 
     return 0
 

examples/servers/simple-auth/mcp_simple_auth/legacy_as_server.py

@@ -66,11 +66,11 @@ def create_simple_mcp_server(server_settings: ServerSettings, auth_settings: Sim
         name="Simple Auth MCP Server",
         instructions="A simple MCP server with simple credential authentication",
         auth_server_provider=oauth_provider,
-        host=server_settings.host,
-        port=server_settings.port,
         debug=True,
         auth=mcp_auth_settings,
     )
+    # Store server settings for later use in run()
+    app._server_settings = server_settings  # type: ignore[attr-defined]
 
     @app.custom_route("/login", methods=["GET"])
     async def login_page_handler(request: Request) -> Response:
@@ -131,7 +131,7 @@ def main(port: int, transport: Literal["sse", "streamable-http"]) -> int:
 
     mcp_server = create_simple_mcp_server(server_settings, auth_settings)
     logger.info(f"🚀 MCP Legacy Server running on {server_url}")
-    mcp_server.run(transport=transport)
+    mcp_server.run(transport=transport, host=host, port=port)
     return 0
 
 

examples/servers/simple-auth/mcp_simple_auth/server.py

@@ -66,8 +66,6 @@ def create_resource_server(settings: ResourceServerSettings) -> FastMCP:
     app = FastMCP(
         name="MCP Resource Server",
         instructions="Resource Server that validates tokens via Authorization Server introspection",
-        host=settings.host,
-        port=settings.port,
         debug=True,
         # Auth configuration for RS mode
         token_verifier=token_verifier,
@@ -77,6 +75,8 @@ def create_resource_server(settings: ResourceServerSettings) -> FastMCP:
             resource_server_url=settings.server_url,
         ),
     )
+    # Store settings for later use in run()
+    app._resource_server_settings = settings  # type: ignore[attr-defined]
 
     @app.tool()
     async def get_time() -> dict[str, Any]:
@@ -153,7 +153,7 @@ def main(port: int, auth_server: str, transport: Literal["sse", "streamable-http
         logger.info(f"🔑 Using Authorization Server: {settings.auth_server_url}")
 
         # Run the server - this should block and keep running
-        mcp_server.run(transport=transport)
+        mcp_server.run(transport=transport, host=host, port=port)
         logger.info("Server stopped")
         return 0
     except Exception:

examples/servers/simple-streamablehttp-stateless/mcp_simple_streamablehttp_stateless/server.py

@@ -6,6 +6,7 @@ from typing import Any
 import anyio
 import click
 import mcp.types as types
+import uvicorn
 from mcp.server.lowlevel import Server
 from mcp.server.streamable_http_manager import StreamableHTTPSessionManager
 from starlette.applications import Starlette
@@ -33,7 +34,7 @@ def main(
     port: int,
     log_level: str,
     json_response: bool,
-) -> int:
+) -> None:
     # Configure logging
     logging.basicConfig(
         level=getattr(logging, log_level.upper()),
@@ -118,9 +119,7 @@ def main(
     # Create an ASGI application using the transport
     starlette_app = Starlette(
         debug=True,
-        routes=[
-            Mount("/mcp", app=handle_streamable_http),
-        ],
+        routes=[Mount("/mcp", app=handle_streamable_http)],
         lifespan=lifespan,
     )
 
@@ -133,8 +132,4 @@ def main(
         expose_headers=["Mcp-Session-Id"],
     )
 
-    import uvicorn
-
     uvicorn.run(starlette_app, host="127.0.0.1", port=port)
-
-    return 0