Edit your Post
<%= form_for @post, :html => {:'data-widget' => 'form', :'data-widget-ajax' => false,
:'data-widget-validators' => ActiveSupport::JSON.encode({'#post_title' => 'not_empty'})} do |f| %>
<%= f.label :email %>
<%= f.error_message_on :email %>
<%= f.text_field :email, :'data-widget-validator' => 'not_empty' %>
<%= f.label :title %>
<%= f.error_message_on :title %>
<%= f.text_field :title %>
<%= f.label :message %>
<%= f.error_message_on :message %>
<%= f.text_area :message %>
<%= f.submit %>
<% end %>