improve duck duck go tool (#13165)

libs/langchain/langchain/tools/ddg_search/tool.py

@@ -1,14 +1,18 @@
 """Tool for the DuckDuckGo search API."""
 
 import warnings
-from typing import Any, Optional
+from typing import Any, Optional, Type
 
 from langchain.callbacks.manager import CallbackManagerForToolRun
-from langchain.pydantic_v1 import Field
+from langchain.pydantic_v1 import BaseModel, Field
 from langchain.tools.base import BaseTool
 from langchain.utilities.duckduckgo_search import DuckDuckGoSearchAPIWrapper
 
 
+class DDGInput(BaseModel):
+    query: str = Field(description="search query to look up")
+
+
 class DuckDuckGoSearchRun(BaseTool):
     """Tool that queries the DuckDuckGo search API."""
 
@@ -21,6 +25,7 @@ class DuckDuckGoSearchRun(BaseTool):
     api_wrapper: DuckDuckGoSearchAPIWrapper = Field(
         default_factory=DuckDuckGoSearchAPIWrapper
     )
+    args_schema: Type[BaseModel] = DDGInput
 
     def _run(
         self,
@@ -45,6 +50,7 @@ class DuckDuckGoSearchResults(BaseTool):
         default_factory=DuckDuckGoSearchAPIWrapper
     )
     backend: str = "api"
+    args_schema: Type[BaseModel] = DDGInput
 
     def _run(
         self,