fix: keep FastMCP from configuring app logging

Author: Genmin

src/mcp/cli/cli.py

@@ -6,7 +6,7 @@
 import subprocess
 import sys
 from pathlib import Path
-from typing import Annotated, Any
+from typing import Annotated, Any, Literal
 
 from mcp.server import MCPServer
 from mcp.server import Server as LowLevelServer
@@ -19,7 +19,7 @@
 
 try:
     from mcp.cli import claude
-    from mcp.server.mcpserver.utilities.logging import get_logger
+    from mcp.server.mcpserver.utilities.logging import configure_logging, get_logger
 except ImportError:  # pragma: no cover
     print("Error: mcp.server is not installed or not in PYTHONPATH")
     sys.exit(1)
@@ -31,6 +31,8 @@
 
 logger = get_logger("cli")
 
+LogLevel = Literal["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"]
+
 app = typer.Typer(
     name="mcp",
     help="MCP development tools",
@@ -116,6 +118,14 @@ def _parse_file_path(file_spec: str) -> tuple[Path, str | None]:
     return file_path, server_object
 
 
+def _get_server_log_level(server: Any) -> LogLevel:
+    settings = getattr(server, "settings", None)
+    log_level = getattr(settings, "log_level", "INFO")
+    if log_level in ("DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"):
+        return log_level
+    return "INFO"
+
+
 def _import_server(file: Path, server_object: str | None = None):  # pragma: no cover
     """Import an MCP server from a file.
 
@@ -340,6 +350,8 @@ def run(
         # Import and get server object
         server = _import_server(file, server_object)
 
+        configure_logging(_get_server_log_level(server))
+
         # Run the server
         kwargs = {}
         if transport:

src/mcp/server/mcpserver/server.py

@@ -36,7 +36,7 @@
 from mcp.server.mcpserver.resources import FunctionResource, Resource, ResourceManager
 from mcp.server.mcpserver.tools import Tool, ToolManager
 from mcp.server.mcpserver.utilities.context_injection import find_context_parameter
-from mcp.server.mcpserver.utilities.logging import configure_logging, get_logger
+from mcp.server.mcpserver.utilities.logging import get_logger
 from mcp.server.sse import SseServerTransport
 from mcp.server.stdio import stdio_server
 from mcp.server.streamable_http import EventStore
@@ -203,9 +203,6 @@ def __init__(
             self._token_verifier = ProviderTokenVerifier(auth_server_provider)
         self._custom_starlette_routes: list[Route] = []
 
-        # Configure logging
-        configure_logging(self.settings.log_level)
-
     @property
     def name(self) -> str:
         return self._lowlevel_server.name

tests/cli/test_utils.py

@@ -5,7 +5,12 @@
 
 import pytest
 
-from mcp.cli.cli import _build_uv_command, _get_npx_command, _parse_file_path  # type: ignore[reportPrivateUsage]
+from mcp.cli.cli import (  # type: ignore[reportPrivateUsage]
+    _build_uv_command,
+    _get_npx_command,
+    _parse_file_path,
+    run,
+)
 
 
 @pytest.mark.parametrize(
@@ -38,6 +43,41 @@ def test_parse_file_exit_on_dir(tmp_path: Path):
         _parse_file_path(str(dir_path))
 
 
+def test_run_configures_logging_at_cli_entrypoint(monkeypatch: pytest.MonkeyPatch, tmp_path: Path):
+    """The CLI owns process logging setup; importing or constructing the server does not."""
+    file = tmp_path / "server.py"
+    file.write_text("server = object()")
+    calls: list[tuple[str, Any]] = []
+
+    class Settings:
+        log_level = "DEBUG"
+
+    class ImportedServer:
+        settings = Settings()
+
+        def run(self, **kwargs: Any) -> None:
+            calls.append(("run", kwargs))
+
+    def fake_import_server(*_args: Any) -> ImportedServer:
+        return ImportedServer()
+
+    def fake_configure_logging(level: str) -> None:
+        calls.append(("logging", level))
+
+    monkeypatch.setattr("mcp.cli.cli._import_server", fake_import_server)
+    monkeypatch.setattr(
+        "mcp.cli.cli.configure_logging",
+        fake_configure_logging,
+    )
+
+    run(f"{file}:server", transport="stdio")
+
+    assert calls == [
+        ("logging", "DEBUG"),
+        ("run", {"transport": "stdio"}),
+    ]
+
+
 def test_build_uv_command_minimal():
     """Should emit core command when no extras specified."""
     cmd = _build_uv_command("foo.py")

tests/server/mcpserver/test_server.py

@@ -1,4 +1,5 @@
 import base64
+import logging
 from pathlib import Path
 from typing import Any
 from unittest.mock import AsyncMock, MagicMock, patch
@@ -46,6 +47,18 @@
 
 
 class TestServer:
+    def test_create_server_does_not_configure_application_logging(self, monkeypatch: pytest.MonkeyPatch):
+        calls: list[tuple[tuple[Any, ...], dict[str, Any]]] = []
+
+        def fake_basic_config(*args: Any, **kwargs: Any) -> None:
+            calls.append((args, kwargs))
+
+        monkeypatch.setattr(logging, "basicConfig", fake_basic_config)
+
+        MCPServer("test")
+
+        assert calls == []
+
     async def test_create_server(self):
         mcp = MCPServer(
             title="MCPServer Server",