Create specific ToolNotFoundError for easier handling in multi-tenant environments

Author: DevonFulcher

src/mcp/server/mcpserver/exceptions.py

@@ -17,5 +17,9 @@ class ToolError(MCPServerError):
     """Error in tool operations."""
 
 
+class ToolNotFoundError(ToolError):
+    """Tool not found."""
+
+
 class InvalidSignature(Exception):
     """Invalid signature for use with MCPServer."""

src/mcp/server/mcpserver/tools/tool_manager.py

@@ -3,7 +3,7 @@
 from collections.abc import Callable
 from typing import TYPE_CHECKING, Any
 
-from mcp.server.mcpserver.exceptions import ToolError
+from mcp.server.mcpserver.exceptions import ToolNotFoundError
 from mcp.server.mcpserver.tools.base import Tool
 from mcp.server.mcpserver.utilities.logging import get_logger
 from mcp.types import Icon, ToolAnnotations
@@ -74,7 +74,7 @@ def add_tool(
     def remove_tool(self, name: str) -> None:
         """Remove a tool by name."""
         if name not in self._tools:
-            raise ToolError(f"Unknown tool: {name}")
+            raise ToolNotFoundError(f"Unknown tool: {name}")
         del self._tools[name]
 
     async def call_tool(
@@ -87,6 +87,6 @@ async def call_tool(
         """Call a tool by name with arguments."""
         tool = self.get_tool(name)
         if not tool:
-            raise ToolError(f"Unknown tool: {name}")
+            raise ToolNotFoundError(f"Unknown tool: {name}")
 
         return await tool.run(arguments, context, convert_result=convert_result)

tests/server/mcpserver/test_server.py

@@ -13,7 +13,7 @@
 from mcp.server.context import ServerRequestContext
 from mcp.server.experimental.request_context import Experimental
 from mcp.server.mcpserver import Context, MCPServer
-from mcp.server.mcpserver.exceptions import ToolError
+from mcp.server.mcpserver.exceptions import ToolError, ToolNotFoundError
 from mcp.server.mcpserver.prompts.base import Message, UserMessage
 from mcp.server.mcpserver.resources import FileResource, FunctionResource
 from mcp.server.mcpserver.utilities.types import Audio, Image
@@ -636,6 +636,13 @@ async def test_remove_nonexistent_tool(self):
         with pytest.raises(ToolError, match="Unknown tool: nonexistent"):
             mcp.remove_tool("nonexistent")
 
+    async def test_remove_nonexistent_tool_raises_tool_not_found_error(self):
+        """Test that removing a non-existent tool raises ToolNotFoundError."""
+        mcp = MCPServer()
+
+        with pytest.raises(ToolNotFoundError, match="Unknown tool: nonexistent"):
+            mcp.remove_tool("nonexistent")
+
     async def test_remove_tool_and_list(self):
         """Test that a removed tool doesn't appear in list_tools."""
         mcp = MCPServer()

tests/server/mcpserver/test_tool_manager.py

@@ -8,7 +8,7 @@
 
 from mcp.server.context import LifespanContextT, RequestT
 from mcp.server.mcpserver import Context, MCPServer
-from mcp.server.mcpserver.exceptions import ToolError
+from mcp.server.mcpserver.exceptions import ToolError, ToolNotFoundError
 from mcp.server.mcpserver.tools import Tool, ToolManager
 from mcp.server.mcpserver.utilities.func_metadata import ArgModelBase, FuncMetadata
 from mcp.types import TextContent, ToolAnnotations
@@ -820,6 +820,13 @@ def test_remove_nonexistent_tool(self):
         with pytest.raises(ToolError, match="Unknown tool: nonexistent"):
             manager.remove_tool("nonexistent")
 
+    def test_remove_nonexistent_tool_raises_tool_not_found_error(self):
+        """Test removing a non-existent tool raises ToolError."""
+        manager = ToolManager()
+
+        with pytest.raises(ToolNotFoundError, match="Unknown tool: nonexistent"):
+            manager.remove_tool("nonexistent")
+
     def test_remove_tool_from_multiple_tools(self):
         """Test removing one tool when multiple tools exist."""
 
@@ -877,6 +884,10 @@ def greet(name: str) -> str:
         with pytest.raises(ToolError, match="Unknown tool: greet"):
             await manager.call_tool("greet", {"name": "World"}, Context())
 
+        # Verify calling removed tool raises ToolNotFoundError
+        with pytest.raises(ToolNotFoundError, match="Unknown tool: greet"):
+            await manager.call_tool("greet", {"name": "World"}, Context())
+
     def test_remove_tool_case_sensitive(self):
         """Test that tool removal is case-sensitive."""
 
@@ -894,6 +905,10 @@ def test_func() -> str:  # pragma: no cover
         with pytest.raises(ToolError, match="Unknown tool: Test_Func"):
             manager.remove_tool("Test_Func")
 
+        # Try to remove with different case - should raise ToolNotFoundError
+        with pytest.raises(ToolNotFoundError, match="Unknown tool: Test_Func"):
+            manager.remove_tool("Test_Func")
+
         # Verify original tool still exists
         assert manager.get_tool("test_func") is not None