diff --git a/eval_protocol/pytest/parameterize.py b/eval_protocol/pytest/parameterize.py
index f8c12259..7892d9c5 100644
--- a/eval_protocol/pytest/parameterize.py
+++ b/eval_protocol/pytest/parameterize.py
@@ -73,6 +73,9 @@ def _is_pytest_parametrize_with_completion_params(decorator: ast.expr) -> bool:
                 and decorator.func.value.attr == "mark"
                 and decorator.func.attr == "parametrize"
             ):
+                # Validate argvalues if present
+                _validate_parametrize_argvalues(decorator)
+
                 # Check positional arguments first (argnames is typically the first positional arg)
                 if len(decorator.args) > 0:
                     argnames_arg = decorator.args[0]
@@ -88,6 +91,90 @@ def _is_pytest_parametrize_with_completion_params(decorator: ast.expr) -> bool:
     return False
 
 
+def _ast_dict_to_string(dict_node: ast.Dict) -> str:
+    """
+    Convert an AST Dict node to its string representation.
+
+    Args:
+        dict_node: AST node representing a dictionary
+
+    Returns:
+        String representation of the dictionary
+    """
+    if not dict_node.keys:
+        return "{}"
+
+    pairs = []
+    for key, value in zip(dict_node.keys, dict_node.values):
+        if key is not None:
+            key_str = _ast_node_to_string(key)
+            value_str = _ast_node_to_string(value)
+            pairs.append(f"{key_str}: {value_str}")
+
+    return "{" + ", ".join(pairs) + "}"
+
+
+def _ast_node_to_string(node: ast.expr) -> str:
+    """
+    Convert an AST node to its string representation.
+
+    Args:
+        node: AST node to convert
+
+    Returns:
+        String representation of the node
+    """
+    if isinstance(node, ast.Constant):
+        if isinstance(node.value, str):
+            return repr(node.value)
+        else:
+            return str(node.value)
+    elif isinstance(node, ast.Name):
+        return node.id
+    elif isinstance(node, ast.Dict):
+        return _ast_dict_to_string(node)
+    elif isinstance(node, ast.List):
+        elements = [_ast_node_to_string(elt) for elt in node.elts]
+        return "[" + ", ".join(elements) + "]"
+    elif isinstance(node, ast.Tuple):
+        elements = [_ast_node_to_string(elt) for elt in node.elts]
+        return "(" + ", ".join(elements) + ")"
+    else:
+        # For complex expressions, return a simplified representation
+        return "<complex expression>"
+
+
+def _validate_parametrize_argvalues(decorator: ast.Call) -> None:
+    """
+    Validate that pytest.mark.parametrize argvalues is a list/tuple, not a dict.
+
+    Args:
+        decorator: AST node representing the pytest.mark.parametrize decorator call
+
+    Raises:
+        ValueError: If argvalues is a dict instead of a list/tuple
+    """
+    # Check positional arguments (argvalues is typically the second positional arg)
+    if len(decorator.args) > 1:
+        argvalues_arg = decorator.args[1]
+        if isinstance(argvalues_arg, ast.Dict):
+            dict_repr = _ast_dict_to_string(argvalues_arg)
+            raise ValueError(
+                f"For evaluation_test with completion_params, pytest.mark.parametrize argvalues must be a list or tuple, not a dict. "
+                f"Use [{dict_repr}] instead of {dict_repr}."
+            )
+
+    # Check keyword arguments for argvalues
+    for keyword in decorator.keywords:
+        if keyword.arg == "argvalues":
+            if isinstance(keyword.value, ast.Dict):
+                dict_repr = _ast_dict_to_string(keyword.value)
+                raise ValueError(
+                    f"For evaluation_test with completion_params, pytest.mark.parametrize argvalues must be a list or tuple, not a dict. "
+                    f"Use [{dict_repr}] instead of {dict_repr}."
+                )
+
+
 def _check_argnames_for_completion_params(argnames_node: ast.expr) -> bool:
     """
     Check if an argnames AST node contains "completion_params".
diff --git a/tests/pytest/test_parameterize_validation.py b/tests/pytest/test_parameterize_validation.py
new file mode 100644
index 00000000..b116965d
--- /dev/null
+++ b/tests/pytest/test_parameterize_validation.py
@@ -0,0 +1,226 @@
+"""
+Test cases for pytest.mark.parametrize validation functionality.
+"""
+
+import ast
+import pytest
+from eval_protocol.pytest.parameterize import _is_pytest_parametrize_with_completion_params
+
+
+def create_parametrize_decorator(argnames, argvalues, use_keyword=False):
+    """Create a pytest.mark.parametrize decorator AST node."""
+    pytest_name = ast.Name(id="pytest", ctx=ast.Load())
+    mark_attr = ast.Attribute(value=pytest_name, attr="mark", ctx=ast.Load())
+    parametrize_attr = ast.Attribute(value=mark_attr, attr="parametrize", ctx=ast.Load())
+
+    if use_keyword:
+        call = ast.Call(
+            func=parametrize_attr,
+            args=[],
+            keywords=[
+                ast.keyword(arg="argnames", value=ast.Constant(value=argnames)),
+                ast.keyword(arg="argvalues", value=argvalues),
+            ],
+        )
+    else:
+        call = ast.Call(func=parametrize_attr, args=[ast.Constant(value=argnames), argvalues], keywords=[])
+
+    return call
+
+
+class TestParametrizeValidation:
+    """Test cases for pytest.mark.parametrize validation."""
+
+    def test_invalid_dict_argvalues_positional(self):
+        """Test that a dict as positional argvalues throws an error."""
+        decorator = create_parametrize_decorator(
+            "completion_params", ast.Dict(keys=[ast.Constant(value="model")], values=[ast.Constant(value="gpt-4")])
+        )
+
+        with pytest.raises(ValueError) as exc_info:
+            _is_pytest_parametrize_with_completion_params(decorator)
+
+        error_msg = str(exc_info.value)
+        assert (
+            "For evaluation_test with completion_params, pytest.mark.parametrize argvalues must be a list or tuple, not a dict"
+            in error_msg
+        )
+        assert "Use [{'model': 'gpt-4'}] instead of {'model': 'gpt-4'}" in error_msg
+
+    def test_valid_list_argvalues_positional(self):
+        """Test that a list as positional argvalues works correctly."""
+        dict_value = ast.Dict(keys=[ast.Constant(value="model")], values=[ast.Constant(value="gpt-4")])
+        list_value = ast.List(elts=[dict_value], ctx=ast.Load())
+
+        decorator = create_parametrize_decorator("completion_params", list_value)
+
+        result = _is_pytest_parametrize_with_completion_params(decorator)
+        assert result is True
+
+    def test_invalid_dict_argvalues_keyword(self):
+        """Test that a dict as keyword argvalues throws an error."""
+        decorator = create_parametrize_decorator(
+            "completion_params",
+            ast.Dict(keys=[ast.Constant(value="model")], values=[ast.Constant(value="gpt-4")]),
+            use_keyword=True,
+        )
+
+        with pytest.raises(ValueError) as exc_info:
+            _is_pytest_parametrize_with_completion_params(decorator)
+
+        error_msg = str(exc_info.value)
+        assert (
+            "For evaluation_test with completion_params, pytest.mark.parametrize argvalues must be a list or tuple, not a dict"
+            in error_msg
+        )
+        assert "Use [{'model': 'gpt-4'}] instead of {'model': 'gpt-4'}" in error_msg
+
+    def test_valid_list_argvalues_keyword(self):
+        """Test that a list as keyword argvalues works correctly."""
+        dict_value = ast.Dict(keys=[ast.Constant(value="model")], values=[ast.Constant(value="gpt-4")])
+        list_value = ast.List(elts=[dict_value], ctx=ast.Load())
+
+        decorator = create_parametrize_decorator("completion_params", list_value, use_keyword=True)
+
+        result = _is_pytest_parametrize_with_completion_params(decorator)
+        assert result is True
+
+    def test_dynamic_error_simple_dict(self):
+        """Test dynamic error message with a simple dict."""
+        decorator = create_parametrize_decorator(
+            "completion_params", ast.Dict(keys=[ast.Constant(value="model")], values=[ast.Constant(value="gpt-4")])
+        )
+
+        with pytest.raises(ValueError) as exc_info:
+            _is_pytest_parametrize_with_completion_params(decorator)
+
+        error_msg = str(exc_info.value)
+        assert (
+            "For evaluation_test with completion_params, pytest.mark.parametrize argvalues must be a list or tuple, not a dict"
+            in error_msg
+        )
+        assert "Use [{'model': 'gpt-4'}] instead of {'model': 'gpt-4'}" in error_msg
+
+    def test_dynamic_error_complex_dict(self):
+        """Test dynamic error message with a complex dict."""
+        decorator = create_parametrize_decorator(
+            "completion_params",
+            ast.Dict(
+                keys=[
+                    ast.Constant(value="model"),
+                    ast.Constant(value="temperature"),
+                    ast.Constant(value="max_tokens"),
+                ],
+                values=[
+                    ast.Constant(value="accounts/fireworks/models/gpt-oss-120b"),
+                    ast.Constant(value=0.7),
+                    ast.Constant(value=1000),
+                ],
+            ),
+        )
+
+        with pytest.raises(ValueError) as exc_info:
+            _is_pytest_parametrize_with_completion_params(decorator)
+
+        error_msg = str(exc_info.value)
+        assert (
+            "For evaluation_test with completion_params, pytest.mark.parametrize argvalues must be a list or tuple, not a dict"
+            in error_msg
+        )
+        assert "Use [{" in error_msg
+        assert "}] instead of {" in error_msg
+        assert "gpt-oss-120b" in error_msg
+        assert "0.7" in error_msg
+        assert "1000" in error_msg
+
+    def test_dynamic_error_nested_dict(self):
+        """Test dynamic error message with nested structures."""
+        # Create a dict with nested dict
+        nested_dict = ast.Dict(
+            keys=[ast.Constant(value="config")],
+            values=[
+                ast.Dict(
+                    keys=[ast.Constant(value="model"), ast.Constant(value="api_key")],
+                    values=[ast.Constant(value="gpt-4"), ast.Constant(value="sk-123")],
+                )
+            ],
+        )
+
+        decorator = create_parametrize_decorator("completion_params", nested_dict)
+
+        with pytest.raises(ValueError) as exc_info:
+            _is_pytest_parametrize_with_completion_params(decorator)
+
+        error_msg = str(exc_info.value)
+        assert (
+            "For evaluation_test with completion_params, pytest.mark.parametrize argvalues must be a list or tuple, not a dict"
+            in error_msg
+        )
+        assert "Use [{" in error_msg
+        assert "}] instead of {" in error_msg
+
+    def test_dynamic_error_boolean_values(self):
+        """Test dynamic error message with boolean values."""
+        decorator = create_parametrize_decorator(
+            "completion_params",
+            ast.Dict(
+                keys=[ast.Constant(value="stream"), ast.Constant(value="echo")],
+                values=[ast.Constant(value=True), ast.Constant(value=False)],
+            ),
+        )
+
+        with pytest.raises(ValueError) as exc_info:
+            _is_pytest_parametrize_with_completion_params(decorator)
+
+        error_msg = str(exc_info.value)
+        assert (
+            "For evaluation_test with completion_params, pytest.mark.parametrize argvalues must be a list or tuple, not a dict"
+            in error_msg
+        )
+        assert "True" in error_msg
+        assert "False" in error_msg
+
+    def test_dynamic_error_empty_dict(self):
+        """Test dynamic error message with empty dict."""
+        decorator = create_parametrize_decorator("completion_params", ast.Dict(keys=[], values=[]))
+
+        with pytest.raises(ValueError) as exc_info:
+            _is_pytest_parametrize_with_completion_params(decorator)
+
+        error_msg = str(exc_info.value)
+        assert (
+            "For evaluation_test with completion_params, pytest.mark.parametrize argvalues must be a list or tuple, not a dict"
+            in error_msg
+        )
+        assert "Use [{}] instead of {}" in error_msg
+
+    def test_valid_tuple_argvalues(self):
+        """Test that a tuple as argvalues works correctly."""
+        dict_value = ast.Dict(keys=[ast.Constant(value="model")], values=[ast.Constant(value="gpt-4")])
+        tuple_value = ast.Tuple(elts=[dict_value], ctx=ast.Load())
+
+        decorator = create_parametrize_decorator("completion_params", tuple_value)
+
+        result = _is_pytest_parametrize_with_completion_params(decorator)
+        assert result is True
+
+    def test_non_parametrize_decorator(self):
+        """Test that non-parametrize decorators are ignored."""
+        # Create a different decorator
+        pytest_name = ast.Name(id="pytest", ctx=ast.Load())
+        mark_attr = ast.Attribute(value=pytest_name, attr="mark", ctx=ast.Load())
+        skipif_attr = ast.Attribute(value=mark_attr, attr="skipif", ctx=ast.Load())
+
+        decorator = ast.Call(func=skipif_attr, args=[ast.Constant(value=True)], keywords=[])
+
+        result = _is_pytest_parametrize_with_completion_params(decorator)
+        assert result is False
+
+    def test_parametrize_without_completion_params(self):
+        """Test that parametrize without completion_params is ignored."""
+        decorator = create_parametrize_decorator(
+            "other_param", ast.List(elts=[ast.Constant(value="value")], ctx=ast.Load())
+        )
+
+        result = _is_pytest_parametrize_with_completion_params(decorator)
+        assert result is False