diff --git a/simplemind/chains/reverse_text.py b/simplemind/chains/reverse_text.py
index 7f102a2..cccdcbc 100644
--- a/simplemind/chains/reverse_text.py
+++ b/simplemind/chains/reverse_text.py
@@ -2,5 +2,24 @@ from .base import BaseChain
 
 
 class ReverseTextChain(BaseChain):
-    def run(self, input_data):
+    """Chain that reverses input text.
+
+    This chain takes a text input and returns it reversed. For example,
+    "hello" becomes "olleh".
+    """
+
+    def run(self, input_data: str) -> str:
+        """Reverse the input text.
+
+        Args:
+            input_data: The text to reverse.
+
+        Returns:
+            The reversed text.
+
+        Raises:
+            TypeError: If input_data is not a string.
+        """
+        if not isinstance(input_data, str):
+            raise TypeError("Input must be a string")
         return input_data[::-1]