diff --git a/zulip_bots/setup.py b/zulip_bots/setup.py
index 6396e29..b71b4d3 100644
--- a/zulip_bots/setup.py
+++ b/zulip_bots/setup.py
@@ -65,6 +65,7 @@ setuptools_info = dict(
         'html2text',
         'lxml',
         'BeautifulSoup4',
+        'typing_extensions',
     ],
 )
 
diff --git a/zulip_bots/zulip_bots/lib.py b/zulip_bots/zulip_bots/lib.py
index 32b69cb..47696be 100644
--- a/zulip_bots/zulip_bots/lib.py
+++ b/zulip_bots/zulip_bots/lib.py
@@ -9,7 +9,7 @@ import re
 
 
 from typing import Any, Optional, List, Dict, IO, Text
-
+from typing_extensions import Protocol
 from zulip import Client, ZulipError
 
 
@@ -102,6 +102,16 @@ class BotIdentity:
         self.email = email
         self.mention = '@**' + name + '**'
 
+class BotStorage(Protocol):
+    def put(self, key: Text, value: Any) -> None:
+        ...
+
+    def get(self, key: Text) -> Any:
+        ...
+
+    def contains(self, key: Text) -> bool:
+        ...
+
 class ExternalBotHandler:
     def __init__(
         self,