diff --git a/queuebie/system_checks/__init__.py b/queuebie/system_checks/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/queuebie/system_checks/handler_return_types.py b/queuebie/system_checks/handler_return_types.py
new file mode 100644
index 0000000..cb1ce76
--- /dev/null
+++ b/queuebie/system_checks/handler_return_types.py
@@ -0,0 +1,56 @@
+import ast
+import logging
+
+from queuebie.logger import get_logger
+
+
+class CommandReturnVisitor(ast.NodeVisitor):
+    """
+    AST visitor to find methods with the `register_command` decorator
+    """
+
+    logger: logging.Logger
+
+    def __init__(self):
+        super().__init__()
+
+        self.logger = get_logger()
+
+    def visit_FunctionDef(self, node): # noqa: N802
+        # Check if the `register_command` decorator is used
+        for decorator in node.decorator_list:
+            if isinstance(decorator, ast.Name) and decorator.id == "register_command":
+                # Check the method's return value
+                if isinstance(node.body[-1], ast.Return):
+                    return_value = node.body[-1].value
+                    # If the return value is a list
+                    if isinstance(return_value, ast.List):
+                        # Verify all elements in the list are of type `queuebie.messages.Command`
+                        if all(
+                            isinstance(elm, ast.Call)
+                            and isinstance(elm.func, ast.Attribute)
+                            and elm.func.attr == "Command"
+                            and isinstance(elm.func.value, ast.Name)
+                            and elm.func.value.id == "queuebie"
+                            for elm in return_value.elts
+                        ):
+                            self.logger.debug(f"{node.name} returns a List[queuebie.messages.Command].")
+                        else:
+                            raise RuntimeError(f"{node.name} returns invalid elements in the list.")
+                    # If the return value is a single `queuebie.messages.Command`
+                    elif isinstance(return_value, ast.Call):
+                        if (
+                            isinstance(return_value.func, ast.Attribute)
+                            and return_value.func.attr == "Command"
+                            and isinstance(return_value.func.value, ast.Name)
+                            and return_value.func.value.id == "queuebie"
+                        ):
+                            self.logger.debug(f"{node.name} returns a single queuebie.messages.Command.")
+                        else:
+                            raise RuntimeError(f"{node.name} returns an invalid Command type.")
+                    # If the return value is None
+                    elif isinstance(return_value, ast.NameConstant) and return_value.value is None:
+                        self.logger.debug(f"{node.name} returns None.")
+                    else:
+                        raise RuntimeError(f"{node.name} returns an invalid Command type.")
+        self.generic_visit(node)
diff --git a/tests/system_checks/__init__.py b/tests/system_checks/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/system_checks/test_handler_return_types.py b/tests/system_checks/test_handler_return_types.py
new file mode 100644
index 0000000..e62c731
--- /dev/null
+++ b/tests/system_checks/test_handler_return_types.py
@@ -0,0 +1,41 @@
+import ast
+
+from queuebie.system_checks.handler_return_types import CommandReturnVisitor
+
+
+def test_handler_returns_single_command():
+#     code = """@register_command
+# def another_method():
+#     return Command()
+#     """
+
+    code = """
+from some_module import register_command
+from queuebie.messages import Command
+
+@register_command
+def some_method():
+    return [Command(), Command()]
+
+@register_command
+def another_method():
+    return Command()
+
+@register_command
+def none_method():
+    return None
+
+@register_command
+def invalid_method():
+    return "invalid"
+
+@register_command
+def wrong_command_method():
+    from another_module import Command
+    return Command()
+"""
+
+    tree = ast.parse(code)
+
+    visitor = CommandReturnVisitor()
+    visitor.visit(tree)