Python: Normalize MCP function names to allowed tool calling values. Add tests.

python/semantic_kernel/connectors/mcp.py

@@ -3,6 +3,7 @@
 import asyncio
 import json
 import logging
+import re
 import sys
 from abc import abstractmethod
 from collections.abc import Callable, Sequence
@@ -177,6 +178,12 @@ def _get_parameter_dicts_from_mcp_tool(tool: types.Tool) -> list[dict[str, Any]]
     return params
 
 
+@experimental
+def _normalize_mcp_name(name: str) -> str:
+    """Normalize MCP tool/prompt names to allowed identifier pattern (A-Za-z0-9_.-)."""
+    return re.sub(r"[^A-Za-z0-9_.-]", "-", name)
+
+
 # region: MCP Plugin
 
 
@@ -366,11 +373,12 @@ async def load_prompts(self):
         except Exception:
             prompt_list = None
         for prompt in prompt_list.prompts if prompt_list else []:
-            func = kernel_function(name=prompt.name, description=prompt.description)(
+            local_name = _normalize_mcp_name(prompt.name)
+            func = kernel_function(name=local_name, description=prompt.description)(
                 partial(self.get_prompt, prompt.name)
             )
             func.__kernel_function_parameters__ = _get_parameter_dict_from_mcp_prompt(prompt)
-            setattr(self, prompt.name, func)
+            setattr(self, local_name, func)
 
     async def load_tools(self):
         """Load tools from the MCP server."""
@@ -380,9 +388,10 @@ async def load_tools(self):
             tool_list = None
             # Create methods with the kernel_function decorator for each tool
         for tool in tool_list.tools if tool_list else []:
-            func = kernel_function(name=tool.name, description=tool.description)(partial(self.call_tool, tool.name))
+            local_name = _normalize_mcp_name(tool.name)
+            func = kernel_function(name=local_name, description=tool.description)(partial(self.call_tool, tool.name))
             func.__kernel_function_parameters__ = _get_parameter_dicts_from_mcp_tool(tool)
-            setattr(self, tool.name, func)
+            setattr(self, local_name, func)
 
     async def close(self) -> None:
         """Disconnect from the MCP server."""

python/tests/unit/connectors/mcp/test_mcp.py

@@ -1,4 +1,6 @@
 # Copyright (c) Microsoft. All rights reserved.
+
+import re
 from typing import TYPE_CHECKING
 from unittest.mock import AsyncMock, MagicMock, patch
 
@@ -12,6 +14,24 @@
     from semantic_kernel import Kernel
 
 
+@pytest.fixture
+def list_tool_calls_with_slash() -> ListToolsResult:
+    return ListToolsResult(
+        tools=[
+            Tool(
+                name="nasa/get-astronomy-picture",
+                description="func with slash",
+                inputSchema={"properties": {}, "required": []},
+            ),
+            Tool(
+                name="weird\\name with spaces",
+                description="func with backslash and spaces",
+                inputSchema={"properties": {}, "required": []},
+            ),
+        ]
+    )
+
+
 @pytest.fixture
 def list_tool_calls() -> ListToolsResult:
     return ListToolsResult(
@@ -230,3 +250,44 @@ async def test_kernel_as_mcp_server(kernel: "Kernel", decorated_native_function,
     assert types.ListToolsRequest in server.request_handlers
     assert types.CallToolRequest in server.request_handlers
     assert server.name == "Semantic Kernel MCP Server"
+
+
+@patch("semantic_kernel.connectors.mcp.sse_client")
+@patch("semantic_kernel.connectors.mcp.ClientSession")
+async def test_mcp_tool_name_normalization(mock_session, mock_client, list_tool_calls_with_slash, kernel: "Kernel"):
+    """Test that MCP tool names with illegal characters are normalized."""
+    mock_read = MagicMock()
+    mock_write = MagicMock()
+    mock_generator = MagicMock()
+    mock_generator.__aenter__.return_value = (mock_read, mock_write)
+    mock_generator.__aexit__.return_value = (mock_read, mock_write)
+    mock_client.return_value = mock_generator
+    mock_session.return_value.__aenter__.return_value.list_tools.return_value = list_tool_calls_with_slash
+
+    async with MCPSsePlugin(
+        name="TestMCPPlugin",
+        description="Test MCP Plugin",
+        url="http://localhost:8080/sse",
+    ) as plugin:
+        loaded_plugin = kernel.add_plugin(plugin)
+        # The normalized names:
+        assert "nasa-get-astronomy-picture" in loaded_plugin.functions
+        assert "weird-name-with-spaces" in loaded_plugin.functions
+        # They should not exist with their original (invalid) names:
+        assert "nasa/get-astronomy-picture" not in loaded_plugin.functions
+        assert "weird\\name with spaces" not in loaded_plugin.functions
+
+        normalized_names = list(loaded_plugin.functions.keys())
+        for name in normalized_names:
+            assert re.match(r"^[A-Za-z0-9_.-]+$", name)
+
+
+@patch("semantic_kernel.connectors.mcp.ClientSession")
+async def test_mcp_normalization_function(mock_session, list_tool_calls_with_slash):
+    """Unit test for the normalize_mcp_name function (should exist in codebase)."""
+    from semantic_kernel.connectors.mcp import _normalize_mcp_name
+
+    assert _normalize_mcp_name("nasa/get-astronomy-picture") == "nasa-get-astronomy-picture"
+    assert _normalize_mcp_name("weird\\name with spaces") == "weird-name-with-spaces"
+    assert _normalize_mcp_name("simple_name") == "simple_name"
+    assert _normalize_mcp_name("Name-With.Dots_And-Hyphens") == "Name-With.Dots_And-Hyphens"