feat: add handle_tool_error and handle_validation_error to load_mcp_tools

Author: Chaitanya-Keyal

langchain_mcp_adapters/client.py

@@ -5,15 +5,16 @@
 """
 
 import asyncio
-from collections.abc import AsyncIterator
+from collections.abc import AsyncIterator, Callable
 from contextlib import asynccontextmanager
 from types import TracebackType
 from typing import Any
 
 from langchain_core.documents.base import Blob
 from langchain_core.messages import AIMessage, HumanMessage
-from langchain_core.tools import BaseTool
+from langchain_core.tools import BaseTool, ToolException
 from mcp import ClientSession
+from pydantic import ValidationError
 
 from langchain_mcp_adapters.callbacks import CallbackContext, Callbacks
 from langchain_mcp_adapters.hooks import Hooks
@@ -142,12 +143,22 @@ async def session(
                 await session.initialize()
             yield session
 
-    async def get_tools(self, *, server_name: str | None = None) -> list[BaseTool]:
+    async def get_tools(
+        self,
+        *,
+        server_name: str | None = None,
+        handle_tool_error: bool | str | Callable[[ToolException], str] | None = False,
+        handle_validation_error: (
+            bool | str | Callable[[ValidationError], str] | None
+        ) = False,
+    ) -> list[BaseTool]:
         """Get a list of all tools from all connected servers.
 
         Args:
             server_name: Optional name of the server to get tools from.
                 If None, all tools from all servers will be returned (default).
+            handle_tool_error: Optional error handler for tool execution errors.
+            handle_validation_error: Optional error handler for validation errors.
 
         NOTE: a new session will be created for each tool call
 
@@ -168,6 +179,8 @@ async def get_tools(self, *, server_name: str | None = None) -> list[BaseTool]:
                 callbacks=self.callbacks,
                 server_name=server_name,
                 hooks=self.hooks,
+                handle_tool_error=handle_tool_error,
+                handle_validation_error=handle_validation_error,
             )
 
         all_tools: list[BaseTool] = []
@@ -180,6 +193,8 @@ async def get_tools(self, *, server_name: str | None = None) -> list[BaseTool]:
                     callbacks=self.callbacks,
                     server_name=name,
                     hooks=self.hooks,
+                    handle_tool_error=handle_tool_error,
+                    handle_validation_error=handle_validation_error,
                 )
             )
             load_mcp_tool_tasks.append(load_mcp_tool_task)

langchain_mcp_adapters/tools.py

@@ -4,6 +4,7 @@
 tools, handle tool execution, and manage tool conversion between the two formats.
 """
 
+from collections.abc import Callable
 from typing import Any, cast, get_args
 
 from langchain_core.tools import (
@@ -25,7 +26,7 @@
     TextContent,
 )
 from mcp.types import Tool as MCPTool
-from pydantic import BaseModel, create_model
+from pydantic import BaseModel, ValidationError, create_model
 
 from langchain_mcp_adapters.callbacks import CallbackContext, Callbacks, _MCPCallbacks
 from langchain_mcp_adapters.hooks import CallToolRequestSpec, Hooks, ToolHookContext
@@ -128,6 +129,10 @@ def convert_mcp_tool_to_langchain_tool(
     callbacks: Callbacks | None = None,
     hooks: Hooks | None = None,
     server_name: str | None = None,
+    handle_tool_error: bool | str | Callable[[ToolException], str] | None = False,
+    handle_validation_error: (
+        bool | str | Callable[[ValidationError], str] | None
+    ) = False,
 ) -> BaseTool:
     """Convert an MCP tool to a LangChain tool.
 
@@ -141,6 +146,8 @@ def convert_mcp_tool_to_langchain_tool(
         callbacks: Optional callbacks for handling notifications and events
         hooks: Optional hooks for before/after tool call processing
         server_name: Name of the server this tool belongs to
+        handle_tool_error: Optional error handler for tool execution errors.
+        handle_validation_error: Optional error handler for validation errors.
 
     Returns:
         a LangChain tool
@@ -259,6 +266,8 @@ async def call_tool(
         coroutine=call_tool,
         response_format="content_and_artifact",
         metadata=metadata,
+        handle_tool_error=handle_tool_error,
+        handle_validation_error=handle_validation_error,
     )
 
 
@@ -269,6 +278,10 @@ async def load_mcp_tools(
     callbacks: Callbacks | None = None,
     hooks: Hooks | None = None,
     server_name: str | None = None,
+    handle_tool_error: bool | str | Callable[[ToolException], str] | None = False,
+    handle_validation_error: (
+        bool | str | Callable[[ValidationError], str] | None
+    ) = False,
 ) -> list[BaseTool]:
     """Load all available MCP tools and convert them to LangChain tools.
 
@@ -278,6 +291,8 @@ async def load_mcp_tools(
         callbacks: Optional callbacks for handling notifications and events.
         hooks: Optional hooks for before/after tool call processing.
         server_name: Name of the server these tools belong to.
+        handle_tool_error: Optional error handler for tool execution errors.
+        handle_validation_error: Optional error handler for validation errors.
 
     Returns:
         List of LangChain tools. Tool annotations are returned as part
@@ -317,6 +332,8 @@ async def load_mcp_tools(
             callbacks=callbacks,
             hooks=hooks,
             server_name=server_name,
+            handle_tool_error=handle_tool_error,
+            handle_validation_error=handle_validation_error,
         )
         for tool in tools
     ]