diff --git a/src/crewai/utilities/string_utils.py b/src/crewai/utilities/string_utils.py
index 630512b04..f4527a6dc 100644
--- a/src/crewai/utilities/string_utils.py
+++ b/src/crewai/utilities/string_utils.py
@@ -1,10 +1,38 @@
 import re
-from typing import Any, Dict, List, Optional, Union
+from typing import Any, Dict, Optional
+
+SUPPORTED_PRIMITIVE_TYPES = (str, int, float, bool)
+SUPPORTED_CONTAINER_TYPES = (dict, list)
+SUPPORTED_TYPES = SUPPORTED_PRIMITIVE_TYPES + SUPPORTED_CONTAINER_TYPES
+
+
+def _validate_input_type(val: Any) -> None:
+    """Validates input types recursively (str, int, float, bool, dict, list).
+    
+    Args:
+        val: The value to validate
+        
+    Raises:
+        ValueError: If the value contains unsupported types
+    """
+    if val is None:
+        return
+    if isinstance(val, SUPPORTED_PRIMITIVE_TYPES):
+        return
+    if isinstance(val, SUPPORTED_CONTAINER_TYPES):
+        for item in val.values() if isinstance(val, dict) else val:
+            _validate_input_type(item)
+        return
+    raise ValueError(
+        f"Unsupported type {type(val).__name__} in inputs. "
+        "Only str, int, float, bool, dict, and list are allowed."
+    )
 
 
 def interpolate_only(
     input_string: Optional[str],
-    inputs: Dict[str, Union[str, int, float, Dict[str, Any], List[Any]]],
+    inputs: Dict[str, Any],
+    raise_on_missing: bool = True,
 ) -> str:
     """Interpolate placeholders (e.g., {key}) in a string while leaving JSON untouched.
     Only interpolates placeholders that follow the pattern {variable_name} where
@@ -28,26 +56,11 @@ def interpolate_only(
     from crewai.utilities.serialization import to_serializable
     
     processed_inputs = {}
-    supported_types = (str, int, float, bool, dict, list)
     
     for key, value in inputs.items():
-        if value is None or isinstance(value, supported_types):
-            def validate_type(val: Any) -> None:
-                if val is None:
-                    return
-                if isinstance(val, (str, int, float, bool)):
-                    return
-                if isinstance(val, (dict, list)):
-                    for item in val.values() if isinstance(val, dict) else val:
-                        validate_type(item)
-                    return
-                raise ValueError(
-                    f"Unsupported type {type(val).__name__} in inputs. "
-                    "Only str, int, float, bool, dict, and list are allowed."
-                )
-            
+        if value is None or isinstance(value, SUPPORTED_TYPES):
             try:
-                validate_type(value)
+                _validate_input_type(value)
                 processed_inputs[key] = value
             except ValueError as e:
                 raise ValueError(f"Invalid value for key '{key}': {str(e)}") from e
diff --git a/tests/utilities/test_string_utils.py b/tests/utilities/test_string_utils.py
index 27ba2125c..c5e96c679 100644
--- a/tests/utilities/test_string_utils.py
+++ b/tests/utilities/test_string_utils.py
@@ -182,7 +182,7 @@ class TestInterpolateOnly:
         template = "Hello, {name}!"
         inputs: Dict[str, Any] = {}
 
-        with pytest.raises(ValueError) as excinfo:
+        with pytest.raises(ValueError):
             interpolate_only(template, inputs)