diff --git a/skimage/viewer/plugins/canny.py b/skimage/viewer/plugins/canny.py
index 3431c6af..7c7bfb3b 100644
--- a/skimage/viewer/plugins/canny.py
+++ b/skimage/viewer/plugins/canny.py
@@ -5,6 +5,7 @@ from ..widgets import Slider, ComboBox
 
 
 class CannyPlugin(OverlayPlugin):
+    """Canny filter plugin to show edges of an image."""
 
     name = 'Canny Filter'