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Repository: slimmer

Templating Rack middleware, injects standard header/footer and GOV.UK Components


Relevant manual pages


Slimmer provides Rack middleware for applying a standard header and footer around pages returned by a Ruby (Rack) application.

It does this by taking the page rendered by the application, extracting the contents of a div with id ‘wrapper’ and inserting that into a div with the same id in one of its templates. It also transfers various other details, such as meta, script, and style tags.

View documentation

Use in a Rails app

Slimmer provides a Railtie so no configuration is necessary.


Slimmer makes HTTP requests to static for templates. These are cached using Rails.cache.

Asset tag helpers

To get asset tag helpers to point to your external asset server, add

config.action_controller.asset_host = ""

to application.rb.

Specifying a template

A specific template can be requested by giving its name in the X-Slimmer-Template HTTP header.

In a controller action, you can do this by calling slimmer_template.

class MyController < ApplicationController
  def index
    slimmer_template 'homepage'

There’s also a macro style method which will affect all actions:

class YourController < ApplicationController
  slimmer_template :admin

To get this, include Slimmer::Template in your ApplicationController:

class ApplicationController < ActionController::Base
  include Slimmer::Template

Use in before_action renders

If you have a non-default layout and want to render in a before_action method, note that you may have to explicitly call slimmer_template(:your_template_name) in the action before rendering. Rendering in a before_action immediately stops the action chain, and since slimmer usually calls slimmer_template as an after_action, it would be skipped over (and you’d get the default layout).


Slimmer can be configured with a logger by passing in a logger instance (anything that quacks like an instance of Logger). For example, to log to the Rails log, put the following in an initializer:

YourApp::Application.configure do
  config.slimmer.logger = Rails.logger

Note: This can’t be in application.rb because the Rails logger hasn’t been initialized by then.

Debug logging

By default if you pass in a logger with its log level set to debug, slimmer will dup this logger and reduce the level to info. (Slimmer’s debug logging is very noisy). To prevent this, set the enable_debugging option to true. e.g. for Rails:

YourApp::Application.configure do
  config.slimmer.enable_debugging = true


Add the following code to features/support:

require 'slimmer/cucumber'


Add the following code to spec/spec_helper:

require 'slimmer/rspec'


MIT License