Implement SEP-986: Tool name validation (#1655)

src/mcp/server/fastmcp/tools/base.py

@@ -11,6 +11,7 @@ from pydantic import BaseModel, Field
 from mcp.server.fastmcp.exceptions import ToolError
 from mcp.server.fastmcp.utilities.context_injection import find_context_parameter
 from mcp.server.fastmcp.utilities.func_metadata import FuncMetadata, func_metadata
+from mcp.shared.tool_name_validation import validate_and_warn_tool_name
 from mcp.types import Icon, ToolAnnotations
 
 if TYPE_CHECKING:
@@ -56,6 +57,8 @@ class Tool(BaseModel):
         """Create a Tool from a function."""
         func_name = name or fn.__name__
 
+        validate_and_warn_tool_name(func_name)
+
         if func_name == "<lambda>":
             raise ValueError("You must provide a name for lambda functions")
 

src/mcp/server/lowlevel/server.py

@@ -90,6 +90,7 @@ from mcp.shared.context import RequestContext
 from mcp.shared.exceptions import McpError
 from mcp.shared.message import ServerMessageMetadata, SessionMessage
 from mcp.shared.session import RequestResponder
+from mcp.shared.tool_name_validation import validate_and_warn_tool_name
 
 logger = logging.getLogger(__name__)
 
@@ -422,6 +423,7 @@ class Server(Generic[LifespanResultT, RequestT]):
                 if isinstance(result, types.ListToolsResult):  # pragma: no cover
                     # Refresh the tool cache with returned tools
                     for tool in result.tools:
+                        validate_and_warn_tool_name(tool.name)
                         self._tool_cache[tool.name] = tool
                     return types.ServerResult(result)
                 else:
@@ -429,6 +431,7 @@ class Server(Generic[LifespanResultT, RequestT]):
                     # Clear and refresh the entire tool cache
                     self._tool_cache.clear()
                     for tool in result:
+                        validate_and_warn_tool_name(tool.name)
                         self._tool_cache[tool.name] = tool
                     return types.ServerResult(types.ListToolsResult(tools=result))