I found this code in another post: # clean string to remove spaces and force lowercase def self.clean_string(string) (string.downcase).gsub(" ","") end My form: <% form_for @post, :html => { :multipart => true } do |f| %> #... <%= f.label 'Topic' %><br /> <%= f.text_field :tag_list %> #... <% end %> I could use something like this in a callback to remove commas from the input on the text_field correct?