From acd1d71e52d4671750b001dc37398115c7336e4d Mon Sep 17 00:00:00 2001
From: Manohar Paturi <186662190+ManoharPaturi@users.noreply.github.com>
Date: Wed, 23 Sep 2026 19:07:29 +0530
Subject: [PATCH] fix(eval): validate tool_names and mode in tool_called_check

Signed-off-by: Manohar Paturi <186662190+ManoharPaturi@users.noreply.github.com>
---
 .../core/agent_framework/_evaluation.py       | 10 ++++++++++
 .../core/tests/core/test_local_eval.py        | 19 +++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/python/packages/core/agent_framework/_evaluation.py b/python/packages/core/agent_framework/_evaluation.py
index 1c57b9f72d8..eeac08f8ff8 100644
--- a/python/packages/core/agent_framework/_evaluation.py
+++ b/python/packages/core/agent_framework/_evaluation.py
@@ -1064,12 +1064,22 @@ def tool_called_check(*tool_names: str, mode: Literal["all", "any"] = "all") ->
     Returns:
         A check function for use with ``LocalEvaluator``.
 
+    Raises:
+        ValueError: If no tool names are provided, if any tool name is not a non-empty string,
+            or if mode is not 'all' or 'any'.
+
     Example:
 
     .. code-block:: python
 
         check = tool_called_check("get_weather", "get_flight_price")
     """
+    if not tool_names:
+        raise ValueError("At least one tool name must be provided to tool_called_check.")
+    if any(not isinstance(t, str) or not t.strip() for t in tool_names):
+        raise ValueError("Tool names must be non-empty strings.")
+    if mode not in ("all", "any"):
+        raise ValueError(f"Invalid mode: {mode!r}. Must be 'all' or 'any'.")
 
     def _check(item: EvalItem) -> CheckResult:
         expected = set(tool_names)
diff --git a/python/packages/core/tests/core/test_local_eval.py b/python/packages/core/tests/core/test_local_eval.py
index 9875b2aeeee..87021a830e8 100644
--- a/python/packages/core/tests/core/test_local_eval.py
+++ b/python/packages/core/tests/core/test_local_eval.py
@@ -973,6 +973,25 @@ async def test_any_mode_none_called(self):
         assert "None of expected tools" in result.reason  # type: ignore[union-attr]  # ty: ignore[unresolved-attribute]
 
 
+class TestToolCalledCheckValidation:
+    """Tests for tool_called_check argument validation."""
+
+    def test_tool_called_check_requires_at_least_one_tool(self):
+        with pytest.raises(ValueError, match="At least one tool name"):
+            tool_called_check()
+
+    def test_tool_called_check_rejects_empty_tool_name(self):
+        with pytest.raises(ValueError, match="non-empty strings"):
+            tool_called_check("valid_tool", "")
+
+        with pytest.raises(ValueError, match="non-empty strings"):
+            tool_called_check("   ")
+
+    def test_tool_called_check_rejects_invalid_mode(self):
+        with pytest.raises(ValueError, match="Invalid mode"):
+            tool_called_check("tool_a", mode="invalid")  # type: ignore[arg-type]
+
+
 class TestCoerceResultScoreError:
     """Tests for _coerce_result handling non-numeric score."""