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.prompts import load_mcp_prompt
 from langchain_mcp_adapters.resources import load_mcp_resources
@@ -125,12 +126,22 @@ 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
 
@@ -145,13 +156,23 @@ async def get_tools(self, *, server_name: str | None = None) -> list[BaseTool]:
                     f"expected one of '{list(self.connections.keys())}'"
                 )
                 raise ValueError(msg)
-            return await load_mcp_tools(None, connection=self.connections[server_name])
+            return await load_mcp_tools(
+                None,
+                connection=self.connections[server_name],
+                handle_tool_error=handle_tool_error,
+                handle_validation_error=handle_validation_error,
+            )
 
         all_tools: list[BaseTool] = []
         load_mcp_tool_tasks = []
         for connection in self.connections.values():
             load_mcp_tool_task = asyncio.create_task(
-                load_mcp_tools(None, connection=connection)
+                load_mcp_tools(
+                    None,
+                    connection=connection,
+                    handle_tool_error=handle_tool_error,
+                    handle_validation_error=handle_validation_error,
+                )
             )
             load_mcp_tool_tasks.append(load_mcp_tool_task)
         tools_list = await asyncio.gather(*load_mcp_tool_tasks)

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 (
@@ -18,7 +19,7 @@
 from mcp.server.fastmcp.utilities.func_metadata import ArgModelBase, FuncMetadata
 from mcp.types import CallToolResult, EmbeddedResource, ImageContent, 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.sessions import Connection, create_session
 
@@ -102,6 +103,10 @@ def convert_mcp_tool_to_langchain_tool(
     tool: MCPTool,
     *,
     connection: Connection | 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.
 
@@ -112,6 +117,8 @@ def convert_mcp_tool_to_langchain_tool(
         tool: MCP tool to convert
         connection: Optional connection config to use to create a new session
                     if a `session` is not provided
+        handle_tool_error: Optional error handler for tool execution errors.
+        handle_validation_error: Optional error handler for validation errors.
 
     Returns:
         a LangChain tool
@@ -148,19 +155,27 @@ 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,
     )
 
 
 async def load_mcp_tools(
     session: ClientSession | None,
     *,
     connection: Connection | 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.
 
     Args:
         session: The MCP client session. If None, connection must be provided.
         connection: Connection config to create a new session if session is None.
+        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
@@ -182,7 +197,13 @@ async def load_mcp_tools(
         tools = await _list_all_tools(session)
 
     return [
-        convert_mcp_tool_to_langchain_tool(session, tool, connection=connection)
+        convert_mcp_tool_to_langchain_tool(
+            session,
+            tool,
+            connection=connection,
+            handle_tool_error=handle_tool_error,
+            handle_validation_error=handle_validation_error,
+        )
         for tool in tools
     ]