Responsive Images Plugin for MODX Evolution automatically adds responsive class (ie: img-responsive) to your content images.
With this plugin you don't need to add class to every image loaded with tinymce editor.
Plugin configuration options
Images Folder: Content images folder || default: assets/images/
Responsive class: default responsive class || default: img-responsive
Note: you can use this field to add all your default images classes, ie:
img-responsive img-thumbnail img-rounded
Install with Package Manager or Store module