From 41d1c352709d3a22e192a185bf8632efab788d09 Mon Sep 17 00:00:00 2001
From: Nick Hollon <nick.hollon@langchain.dev>
Date: Wed, 27 May 2026 18:57:19 -0400
Subject: [PATCH] Wire subagent_name through StructuredTool.from_function

StructuredTool.from_function now accepts subagent_name= as a named
parameter and passes it to the constructed StructuredTool instance.
Completes the trio of subagent_name entry points: BaseTool attribute,
@tool decorator, StructuredTool.from_function.
---
 libs/core/langchain_core/tools/structured.py |  4 ++
 libs/core/tests/unit_tests/test_tools.py     | 44 ++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/libs/core/langchain_core/tools/structured.py b/libs/core/langchain_core/tools/structured.py
index 8b67e3b4547..5b7741b6036 100644
--- a/libs/core/langchain_core/tools/structured.py
+++ b/libs/core/langchain_core/tools/structured.py
@@ -143,6 +143,7 @@ class StructuredTool(BaseTool):
         response_format: Literal["content", "content_and_artifact"] = "content",
         parse_docstring: bool = False,
         error_on_invalid_docstring: bool = False,
+        subagent_name: str | Callable[[ToolCall], str] | None = None,
         **kwargs: Any,
     ) -> StructuredTool:
         """Create tool from a given function.
@@ -171,6 +172,8 @@ class StructuredTool(BaseTool):
                 to parse parameter descriptions from Google Style function docstrings.
             error_on_invalid_docstring: if `parse_docstring` is provided, configure
                 whether to raise `ValueError` on invalid Google Style docstrings.
+            subagent_name: Name of the subagent this tool should route to (static
+                string or callable that resolves the name from the `ToolCall`).
             **kwargs: Additional arguments to pass to the tool
 
         Returns:
@@ -248,6 +251,7 @@ class StructuredTool(BaseTool):
             description=description_,
             return_direct=return_direct,
             response_format=response_format,
+            subagent_name=subagent_name,
             **kwargs,
         )
 
diff --git a/libs/core/tests/unit_tests/test_tools.py b/libs/core/tests/unit_tests/test_tools.py
index f53a5801aa2..d5e9b37b60e 100644
--- a/libs/core/tests/unit_tests/test_tools.py
+++ b/libs/core/tests/unit_tests/test_tools.py
@@ -3813,3 +3813,47 @@ def test_tool_decorator_subagent_name_defaults_to_none() -> None:
         return str(x)
 
     assert plain.subagent_name is None
+
+
+# --- StructuredTool.from_function subagent_name passthrough tests ---
+
+
+def test_structured_tool_from_function_passes_subagent_name_static() -> None:
+    def my_func(x: int) -> str:
+        return f"x={x}"
+
+    t = StructuredTool.from_function(
+        func=my_func,
+        name="my_func",
+        description="Test tool for subagent_name passthrough.",
+        subagent_name="x_agent",
+    )
+    assert t.subagent_name == "x_agent"
+
+
+def test_structured_tool_from_function_passes_subagent_name_callable() -> None:
+    def my_func(target: str) -> str:
+        return f"target={target}"
+
+    def resolver(call: ToolCall) -> str:
+        return str(call["args"]["target"])
+
+    t = StructuredTool.from_function(
+        func=my_func,
+        name="my_func",
+        description="Test tool for callable subagent_name.",
+        subagent_name=resolver,
+    )
+    assert t.subagent_name is resolver
+
+
+def test_structured_tool_from_function_subagent_name_defaults_to_none() -> None:
+    def my_func(x: int) -> str:
+        return str(x)
+
+    t = StructuredTool.from_function(
+        func=my_func,
+        name="my_func",
+        description="Plain tool.",
+    )
+    assert t.subagent_name is None