diff --git a/agents/utils/tool_util.py b/agents/utils/tool_util.py
index 763fb749e..cbfeb61fe 100644
--- a/agents/utils/tool_util.py
+++ b/agents/utils/tool_util.py
@@ -11,12 +11,15 @@ async def _execute_single_tool(
     response = {"type": "tool_result", "tool_use_id": call.id}
 
     try:
-        # Execute the tool directly
-        result = await tool_dict[call.name].execute(**call.input)
-        response["content"] = str(result)
+        tool = tool_dict[call.name]
     except KeyError:
         response["content"] = f"Tool '{call.name}' not found"
         response["is_error"] = True
+        return response
+
+    try:
+        result = await tool.execute(**call.input)
+        response["content"] = str(result)
     except Exception as e:
         response["content"] = f"Error executing tool: {str(e)}"
         response["is_error"] = True
diff --git a/tests/agents/test_tool_keyerror_diagnostics.py b/tests/agents/test_tool_keyerror_diagnostics.py
new file mode 100644
index 000000000..24a3e39ec
--- /dev/null
+++ b/tests/agents/test_tool_keyerror_diagnostics.py
@@ -0,0 +1,29 @@
+import asyncio
+from types import SimpleNamespace
+from unittest.mock import AsyncMock
+
+from utils.tool_util import _execute_single_tool
+
+
+def test_execution_keyerror_is_not_reported_as_missing_tool():
+    tool = SimpleNamespace(execute=AsyncMock(side_effect=KeyError("required_field")))
+    call = SimpleNamespace(id="call_1", name="example", input={})
+    result = asyncio.run(_execute_single_tool(call, {"example": tool}))
+    assert result["is_error"] is True
+    assert result["content"] == "Error executing tool: 'required_field'"
+    assert result["tool_use_id"] == "call_1"
+
+
+def test_missing_tool_keeps_lookup_error():
+    call = SimpleNamespace(id="call_1", name="missing", input={})
+    result = asyncio.run(_execute_single_tool(call, {}))
+    assert result["content"] == "Tool 'missing' not found"
+    assert result["is_error"] is True
+
+
+def test_successful_tool_result():
+    tool = SimpleNamespace(execute=AsyncMock(return_value="done"))
+    call = SimpleNamespace(id="call_1", name="example", input={"value": 1})
+    result = asyncio.run(_execute_single_tool(call, {"example": tool}))
+    assert result == {"type": "tool_result", "tool_use_id": "call_1", "content": "done"}
+    tool.execute.assert_awaited_once_with(value=1)
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 000000000..300d79c89
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,4 @@
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "agents"))