diff --git a/moulinette/core.py b/moulinette/core.py
index 4c0bdcf8..6f6fddd7 100644
--- a/moulinette/core.py
+++ b/moulinette/core.py
@@ -246,7 +246,7 @@ class Moulinette18n(object):
         for n in self._namespaces.values():
             n.set_locale(locale)
 
-    def g(self, key, *args, **kwargs):
+    def g(self, key: str, *args, **kwargs) -> str:
         """Retrieve proper translation for a moulinette key
 
         Attempt to retrieve value for a key from moulinette translations
@@ -258,7 +258,7 @@ class Moulinette18n(object):
         """
         return self._global.translate(key, *args, **kwargs)
 
-    def n(self, key, *args, **kwargs):
+    def n(self, key: str, *args, **kwargs) -> str:
         """Retrieve proper translation for a moulinette key
 
         Attempt to retrieve value for a key from current loaded namespace
@@ -271,7 +271,7 @@ class Moulinette18n(object):
         """
         return self._namespaces[self._current_namespace].translate(key, *args, **kwargs)
 
-    def key_exists(self, key):
+    def key_exists(self, key: str) -> bool:
         """Check if a key exists in the translation files
 
         Keyword arguments:
@@ -298,7 +298,7 @@ class MoulinetteError(Exception):
         super(MoulinetteError, self).__init__(msg)
         self.strerror = msg
 
-    def content(self):
+    def content(self) -> str:
         return self.strerror