fix(mcp/): re-raise exception from server to client

allows user to debug why mcp server is not working as expected

Related to #15180

Author: krrishdholakia

litellm/experimental_mcp_client/client.py

@@ -235,10 +235,9 @@ async def list_tools(self) -> List[MCPTool]:
             await self.disconnect()
             raise
         except Exception as e:
-            verbose_logger.warning(f"MCP client list_tools failed: {str(e)}")
+            verbose_logger.debug(f"MCP client list_tools failed: {str(e)}")
             await self.disconnect()
-            # Return empty list instead of raising to allow graceful degradation
-            return []
+            raise e
 
     async def call_tool(
         self, call_tool_request_params: MCPCallToolRequestParams

litellm/proxy/_experimental/mcp_server/mcp_server_manager.py

@@ -490,10 +490,10 @@ async def _get_tools_from_server(
             return prefixed_or_original_tools
 
         except Exception as e:
-            verbose_logger.warning(
+            verbose_logger.debug(
                 f"Failed to get tools from server {server.name}: {str(e)}"
             )
-            return []
+            raise e
         finally:
             if client:
                 try:
@@ -522,14 +522,14 @@ async def _list_tools_task():
                 tools = await client.list_tools()
                 verbose_logger.debug(f"Tools from {server_name}: {tools}")
                 return tools
-            except asyncio.CancelledError:
-                verbose_logger.warning(f"Client operation cancelled for {server_name}")
-                return []
+            except asyncio.CancelledError as e:
+                verbose_logger.debug(f"Client operation cancelled for {server_name}")
+                raise e
             except Exception as e:
-                verbose_logger.warning(
+                verbose_logger.debug(
                     f"Client operation failed for {server_name}: {str(e)}"
                 )
-                return []
+                raise e
             finally:
                 try:
                     await client.disconnect()
@@ -538,22 +538,22 @@ async def _list_tools_task():
 
         try:
             return await asyncio.wait_for(_list_tools_task(), timeout=30.0)
-        except asyncio.TimeoutError:
-            verbose_logger.warning(f"Timeout while listing tools from {server_name}")
-            return []
-        except asyncio.CancelledError:
-            verbose_logger.warning(
+        except asyncio.TimeoutError as e:
+            verbose_logger.debug(f"Timeout while listing tools from {server_name}")
+            raise e
+        except asyncio.CancelledError as e:
+            verbose_logger.debug(
                 f"Task cancelled while listing tools from {server_name}"
             )
-            return []
+            raise e
         except ConnectionError as e:
-            verbose_logger.warning(
+            verbose_logger.debug(
                 f"Connection error while listing tools from {server_name}: {str(e)}"
             )
-            return []
+            raise e
         except Exception as e:
-            verbose_logger.warning(f"Error listing tools from {server_name}: {str(e)}")
-            return []
+            verbose_logger.debug(f"Error listing tools from {server_name}: {str(e)}")
+            raise e
 
     def _create_prefixed_tools(
         self, tools: List[MCPTool], server: MCPServer, add_prefix: bool = True

litellm/proxy/_experimental/mcp_server/server.py

@@ -206,10 +206,8 @@ async def list_tools() -> List[MCPTool]:
             )
             return tools
         except Exception as e:
-            verbose_logger.exception(f"Error in list_tools endpoint: {str(e)}")
-            # Return empty list instead of failing completely
-            # This prevents the HTTP stream from failing and allows the client to get a response
-            return []
+            verbose_logger.debug(f"Error in list_tools endpoint: {str(e)}")
+            raise e
 
     @server.call_tool()
     async def mcp_server_tool_call(
@@ -364,25 +362,25 @@ async def _get_allowed_mcp_servers_from_mcp_server_names(
     def _tool_name_matches(tool_name: str, filter_list: List[str]) -> bool:
         """
         Check if a tool name matches any name in the filter list.
-        
+
         Checks both the full tool name and unprefixed version (without server prefix).
         This allows users to configure simple tool names regardless of prefixing.
-        
+
         Args:
             tool_name: The tool name to check (may be prefixed like "server-tool_name")
             filter_list: List of tool names to match against
-            
+
         Returns:
             True if the tool name (prefixed or unprefixed) is in the filter list
         """
         from litellm.proxy._experimental.mcp_server.utils import (
             get_server_name_prefix_tool_mcp,
         )
-        
+
         # Check if the full name is in the list
         if tool_name in filter_list:
             return True
-            
+
         # Check if the unprefixed name is in the list
         unprefixed_name, _ = get_server_name_prefix_tool_mcp(tool_name)
         return unprefixed_name in filter_list
@@ -393,34 +391,36 @@ def filter_tools_by_allowed_tools(
     ) -> List[MCPTool]:
         """
         Filter tools by allowed/disallowed tools configuration.
-        
+
         If allowed_tools is set, only tools in that list are returned.
         If disallowed_tools is set, tools in that list are excluded.
         Tool names are matched with and without server prefixes for flexibility.
-        
+
         Args:
             tools: List of tools to filter
             mcp_server: Server configuration with allowed_tools/disallowed_tools
-            
+
         Returns:
             Filtered list of tools
         """
         tools_to_return = tools
-        
+
         # Filter by allowed_tools (whitelist)
         if mcp_server.allowed_tools:
             tools_to_return = [
-                tool for tool in tools 
+                tool
+                for tool in tools
                 if _tool_name_matches(tool.name, mcp_server.allowed_tools)
             ]
-                    
+
         # Filter by disallowed_tools (blacklist)
         if mcp_server.disallowed_tools:
             tools_to_return = [
-                tool for tool in tools_to_return
+                tool
+                for tool in tools_to_return
                 if not _tool_name_matches(tool.name, mcp_server.disallowed_tools)
             ]
-            
+
         return tools_to_return
 
     async def _get_tools_from_mcp_servers(
@@ -497,18 +497,19 @@ async def _get_tools_from_mcp_servers(
                     extra_headers=extra_headers,
                     add_prefix=add_prefix,
                 )
-                
+
                 filtered_tools = filter_tools_by_allowed_tools(tools, server)
                 all_tools.extend(filtered_tools)
-                
+
                 verbose_logger.debug(
                     f"Successfully fetched {len(tools)} tools from server {server.name}, {len(filtered_tools)} after filtering"
                 )
             except Exception as e:
-                verbose_logger.exception(
+                verbose_logger.debug(
                     f"Error getting tools from server {server.name}: {str(e)}"
                 )
                 # Continue with other servers instead of failing completely
+                raise e
 
         verbose_logger.info(
             f"Successfully fetched {len(all_tools)} tools total from all MCP servers"
@@ -556,7 +557,7 @@ async def _list_mcp_tools(
                 f"Error getting tools from managed MCP servers: {str(e)}"
             )
             # Continue with empty managed tools list instead of failing completely
-
+            raise e
         # Get tools from local registry
         local_tools = []
         try:

litellm/proxy/_new_secret_config.yaml

@@ -16,18 +16,10 @@ model_list:
       api_base: "https://webhook.site/2f385e05-00aa-402b-86d1-efc9261471a5"
       api_key: dummy
 
-# mcp_servers:
-#   github_mcp:
-#     url: "https://api.githubcopilot.com/mcp"
-#     auth_type: oauth2
-#     authorization_url: https://github.com/login/oauth/authorize
-#     token_url: https://github.com/login/oauth/access_token
-#     client_id: os.environ/GITHUB_OAUTH_CLIENT_ID
-#     client_secret: os.environ/GITHUB_OAUTH_CLIENT_SECRET
-#     scopes: ["public_repo", "user:email"]
-#     allowed_tools: ["list_tools"]
-#     # disallowed_tools: ["repo_delete"]
-
-litellm_settings:
-  callbacks: ["prometheus"]
-  custom_prometheus_metadata_labels: ["metadata.initiative", "metadata.business-unit"]
+mcp_servers:
+  local_fake_mcp:
+    url: "http://127.0.0.1:8001/mcp"
+    transport: "http"
+    description: "My custom MCP server"
+    auth_type: "api_key"
+    auth_value: "abc123"