diff --git a/src/comfydv/format_string.py b/src/comfydv/format_string.py
index 2ba0f40..c934dee 100644
--- a/src/comfydv/format_string.py
+++ b/src/comfydv/format_string.py
@@ -75,6 +75,10 @@ class FormatString:
 
     # Create a sandboxed Jinja2 environment for security
     jinja_env = sandbox.SandboxedEnvironment()
+    # Jinja2 ships `tojson` but not its inverse; add one so STRING inputs
+    # carrying a JSON array/object (ComfyUI has no native list socket type)
+    # can be parsed back into real Python data, e.g. `{{ hints | fromjson }}`.
+    jinja_env.filters["fromjson"] = json.loads
 
     # Define additional context
     @staticmethod
diff --git a/tests/test_format_string.py b/tests/test_format_string.py
index e56a186..3f6bcdc 100644
--- a/tests/test_format_string.py
+++ b/tests/test_format_string.py
@@ -201,6 +201,18 @@ class TestJinja2Formatting:
         assert result[2] == "John"
         assert result[3] == "Doe"
 
+    def test_jinja2_fromjson_filter_parses_array(self, format_string_class):
+        """ComfyUI has no native list socket, so a STRING input carrying a
+        JSON array must be parseable back into a real list for iteration."""
+        result = format_string_class.format_string(
+            template_type="Jinja2",
+            template="{% for hint in hints | fromjson %}- {{ hint }}\n{% endfor %}",
+            save_path="",
+            unique_id="test-fromjson",
+            hints='["motion", "camera pan"]',
+        )["result"]
+        assert result[0] == "- motion\n- camera pan\n"
+
     def test_jinja2_with_datetime(self, format_string_class):
         """Test Jinja2 formatting with datetime context."""
         result = format_string_class.format_string(