From 26669991580f2ef5333e3bb240e32f3e593262f0 Mon Sep 17 00:00:00 2001
From: Ignazio De Santis <ignaziodesantisofficial@gmail.com>
Date: Thu, 26 Mar 2026 21:55:42 +0800
Subject: [PATCH] feat(mcp): expose server name on function tools

---
 src/agents/mcp/util.py      |  1 +
 src/agents/tool.py          |  5 +++++
 tests/mcp/test_mcp_util.py  | 12 ++++++++++++
 tests/test_function_tool.py | 20 ++++++++++++++++++++
 4 files changed, 38 insertions(+)

diff --git a/src/agents/mcp/util.py b/src/agents/mcp/util.py
index 33bea065c5..d143c7a707 100644
--- a/src/agents/mcp/util.py
+++ b/src/agents/mcp/util.py
@@ -313,6 +313,7 @@ def to_function_tool(
             strict_json_schema=is_strict,
             needs_approval=needs_approval,
             mcp_title=resolve_mcp_tool_title(tool),
+            mcp_server_name=server.name,
         )
         return function_tool
 
diff --git a/src/agents/tool.py b/src/agents/tool.py
index 1ac3c29ae3..c860449487 100644
--- a/src/agents/tool.py
+++ b/src/agents/tool.py
@@ -294,6 +294,9 @@ class FunctionTool:
     defer_loading: bool = False
     """Whether the Responses API should hide this tool definition until tool search loads it."""
 
+    mcp_server_name: str | None = field(default=None, kw_only=True)
+    """The MCP server name this tool originated from, if it was converted from an MCP tool."""
+
     _failure_error_function: ToolErrorFunction | None = field(
         default=None,
         kw_only=True,
@@ -428,6 +431,7 @@ def _build_wrapped_function_tool(
     defer_loading: bool = False,
     sync_invoker: bool = False,
     mcp_title: str | None = None,
+    mcp_server_name: str | None = None,
 ) -> FunctionTool:
     """Create a FunctionTool with copied-tool-aware failure handling bound in one place."""
     on_invoke_tool = with_function_tool_failure_error_handler(
@@ -452,6 +456,7 @@ def _build_wrapped_function_tool(
             timeout_behavior=timeout_behavior,
             timeout_error_function=timeout_error_function,
             defer_loading=defer_loading,
+            mcp_server_name=mcp_server_name,
             _mcp_title=mcp_title,
         ),
         failure_error_function,
diff --git a/tests/mcp/test_mcp_util.py b/tests/mcp/test_mcp_util.py
index 5a9cbd140c..b11bda42e4 100644
--- a/tests/mcp/test_mcp_util.py
+++ b/tests/mcp/test_mcp_util.py
@@ -81,6 +81,17 @@ async def test_get_all_function_tools():
     assert len(tools) == 5
     assert all(tool.name in names for tool in tools)
 
+    expected_server_names = [
+        server1.name,
+        server1.name,
+        server2.name,
+        server2.name,
+        server3.name,
+    ]
+    for tool, expected_server_name in zip(tools, expected_server_names):
+        assert isinstance(tool, FunctionTool)
+        assert tool.mcp_server_name == expected_server_name
+
 
 @pytest.mark.asyncio
 async def test_invoke_mcp_tool():
@@ -159,6 +170,7 @@ async def test_to_function_tool_passes_static_mcp_meta():
     )
 
     function_tool = MCPUtil.to_function_tool(tool, server, convert_schemas_to_strict=False)
+    assert function_tool.mcp_server_name == server.name
     tool_context = ToolContext(
         context=None,
         tool_name="test_tool_1",
diff --git a/tests/test_function_tool.py b/tests/test_function_tool.py
index 11eb5d7c2e..c07b935b37 100644
--- a/tests/test_function_tool.py
+++ b/tests/test_function_tool.py
@@ -350,6 +350,7 @@ async def run_function(ctx: RunContextWrapper[Any], args: str) -> str:
 
     assert tool.name == "test"
     assert tool.description == "Processes extracted user data"
+    assert tool.mcp_server_name is None
     for key, value in FunctionArgs.model_json_schema().items():
         assert tool.params_json_schema[key] == value
     assert tool.strict_json_schema
@@ -702,6 +703,25 @@ def boom() -> None:
     assert cast(Any, copied_tool).custom_state is custom_state
 
 
+def test_function_tool_copy_preserves_mcp_server_name() -> None:
+    async def invoke(_ctx: ToolContext[Any], _args: str) -> str:
+        return "ok"
+
+    original_tool = FunctionTool(
+        name="tool_name",
+        description="tool_description",
+        params_json_schema={"type": "object", "properties": {}},
+        on_invoke_tool=invoke,
+        mcp_server_name="filesystem",
+    )
+
+    shallow_copied_tool = copy.copy(original_tool)
+    replaced_tool = dataclasses.replace(original_tool, name="copied_tool")
+
+    assert shallow_copied_tool.mcp_server_name == "filesystem"
+    assert replaced_tool.mcp_server_name == "filesystem"
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize("copy_style", ["replace", "shallow_copy"])
 async def test_copied_function_tool_invalid_input_uses_current_name(copy_style: str) -> None: