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.interceptors import ToolCallInterceptor
@@ -55,6 +56,10 @@ def __init__(
         callbacks: Callbacks | None = None,
         tool_interceptors: list[ToolCallInterceptor] | None = None,
         tool_name_prefix: bool = False,
+        handle_tool_error: bool | str | Callable[[ToolException], str] | None = False,
+        handle_validation_error: (
+            bool | str | Callable[[ValidationError], str] | None
+        ) = False,
     ) -> None:
         """Initialize a `MultiServerMCPClient` with MCP servers connections.
 
@@ -68,6 +73,8 @@ def __init__(
                 using an underscore separator (e.g., `"weather_search"` instead of
                 `"search"`). This helps avoid conflicts when multiple servers have tools
                 with the same name. Defaults to `False`.
+            handle_tool_error: Optional error handler for tool execution errors.
+            handle_validation_error: Optional error handler for validation errors.
 
         !!! example "Basic usage (starting a new session on each tool call)"
 
@@ -110,6 +117,8 @@ def __init__(
         self.callbacks = callbacks or Callbacks()
         self.tool_interceptors = tool_interceptors or []
         self.tool_name_prefix = tool_name_prefix
+        self.handle_tool_error = handle_tool_error
+        self.handle_validation_error = handle_validation_error
 
     @asynccontextmanager
     async def session(
@@ -178,6 +187,8 @@ async def get_tools(self, *, server_name: str | None = None) -> list[BaseTool]:
                 server_name=server_name,
                 tool_interceptors=self.tool_interceptors,
                 tool_name_prefix=self.tool_name_prefix,
+                handle_tool_error=self.handle_tool_error,
+                handle_validation_error=self.handle_validation_error,
             )
 
         all_tools: list[BaseTool] = []
@@ -191,6 +202,8 @@ async def get_tools(self, *, server_name: str | None = None) -> list[BaseTool]:
                     server_name=name,
                     tool_interceptors=self.tool_interceptors,
                     tool_name_prefix=self.tool_name_prefix,
+                    handle_tool_error=self.handle_tool_error,
+                    handle_validation_error=self.handle_validation_error,
                 )
             )
             load_mcp_tool_tasks.append(load_mcp_tool_task)

langchain_mcp_adapters/tools.py

@@ -37,7 +37,7 @@
     TextResourceContents,
 )
 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.interceptors import (
@@ -278,6 +278,10 @@ def convert_mcp_tool_to_langchain_tool(
     tool_interceptors: list[ToolCallInterceptor] | None = None,
     server_name: str | None = None,
     tool_name_prefix: bool = False,
+    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.
 
@@ -293,6 +297,8 @@ def convert_mcp_tool_to_langchain_tool(
         server_name: Name of the server this tool belongs to
         tool_name_prefix: If `True` and `server_name` is provided, the tool name will be
             prefixed w/ server name (e.g., `"weather_search"` instead of `"search"`)
+        handle_tool_error: Optional error handler for tool execution errors.
+        handle_validation_error: Optional error handler for validation errors.
 
     Returns:
         a LangChain tool
@@ -430,6 +436,8 @@ async def execute_tool(request: MCPToolCallRequest) -> MCPToolCallResult:
         coroutine=call_tool,
         response_format="content_and_artifact",
         metadata=metadata,
+        handle_tool_error=handle_tool_error,
+        handle_validation_error=handle_validation_error,
     )
 
 
@@ -441,6 +449,10 @@ async def load_mcp_tools(
     tool_interceptors: list[ToolCallInterceptor] | None = None,
     server_name: str | None = None,
     tool_name_prefix: bool = False,
+    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](https://docs.langchain.com/oss/python/langchain/tools).
 
@@ -452,6 +464,8 @@ async def load_mcp_tools(
         server_name: Name of the server these tools belong to.
         tool_name_prefix: If `True` and `server_name` is provided, tool names will be
             prefixed w/ server name (e.g., `"weather_search"` instead of `"search"`).
+        handle_tool_error: Optional error handler for tool execution errors.
+        handle_validation_error: Optional error handler for validation errors.
 
     Returns:
         List of LangChain [tools](https://docs.langchain.com/oss/python/langchain/tools).
@@ -492,6 +506,8 @@ async def load_mcp_tools(
             tool_interceptors=tool_interceptors,
             server_name=server_name,
             tool_name_prefix=tool_name_prefix,
+            handle_tool_error=handle_tool_error,
+            handle_validation_error=handle_validation_error,
         )
         for tool in tools
     ]