navinspm / act_as_taggable

gem ‘acts-as-taggable-on’

then run 
	rake acts_as_taggable_on_engine:install:migrations
	rake db:migrate

and in your index

	  Tags:<%= raw article.tag_list.map { |t| link_to t, tag_path(t)}.join(',') %><br>

in model

	  acts_as_taggable

in _form add a field

		
		 <div class="field">
  	<%= f.label :tag_list , "Tags(separate by commas"%><br>
  	<%= f.text_field :tag_list %>

in your controller

def index

   		if params[:tag]
     			@articles=Article.tagged_with(params[:tag])
   		else
   			@articles = Article.all
   		end
 		end

 		add :tag_list in your controller_params

to add tag_cloud

   	  	<div id="tag_cloud">
				 <% tag_cloud Article.tag_counts, %w[s m l ] do |tag, css_class | %>
 				<%= link_to tag.name, tag_path(tag.name), class: css_class %>
 				<% end %>
			</div>

			in contoller.css.scss

			#tag_cloud {

width: 400px; line-height: 1.6em; .s {font-size: 0.8em;} .m {font-size: 1.2em;} .l {font-size: 1.8em;} }