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The dynamic stylesheet language for the Rails asset pipeline.

This gem provides integration for Rails projects using the Less stylesheet language in the asset pipeline.


Just bundle up less-rails in your Gemfile. This will pull in less as a runtime dependency too.

gem 'less-rails'


This gem was made for other gems to properly hook into one place to provide paths to the Less::Parser. For example, the less-rails-bootstrap project at and each project should do the path configuration for you. If you need to, you can configure less-rails with additional paths. These paths have higher priority than those from your applications assets load paths.

MyProject::Application.configure do
  config.less.paths << "#{Rails.root}/lib/less/stylesheets"
  config.less.compress = true

About Compression

If config.assets.compress is set to true, we will set the config.assets.css_compressor to for you automatically. Feel free to set the css_compressor to something more stronger like :yui in your config/environments/production.rb file.


When referencing assets use the following helpers in LESS.

asset-path(@relative-asset-path)  /* Returns a string to the asset. */
asset-path("rails.png")           /* Becomes: "/assets/rails.png" */

asset-url(@relative-asset-path)   /* Returns url reference to the asset. */
asset-url("rails.png")            /* Becomes: url(/assets/rails.png) */

As a convenience, for each of the following asset classes there are corresponding -path and -url helpers image, font, video, audio, javascript and stylesheet. The following examples only show the -url variants since you get the idea of the -path ones above.

image-url("rails.png")            /* Becomes: url(/assets/rails.png) */
font-url("rails.ttf")             /* Becomes: url(/assets/rails.ttf) */
video-url("rails.ttf")            /* Becomes: url(/videos/rails.mp4) */
audio-url("rails.ttf")            /* Becomes: url(/audios/rails.mp3) */
javascript-url("rails.js")        /* Becomes: url(/assets/rails.js) */
stylesheet-url("rails.css")       /* Becomes: url(/assets/rails.css) */

Lastly, we provide a data url method for base64 encoding assets.

asset-data-url("rails.png")       /* Becomes: url(data:image/png;base64,iVBORw0K...) */

Please note that these helpers are only available server-side, and something like ERB templates should be used if client-side rendering is desired.


Installation of the gem will set your applications stylesheet engine to use Less. It is possible to have many gems that set the stylesheet engine, for instance the sass-rails and/or stylus gems. In this case, you can resolve the ambiguity by setting the stylesheet engine in your config/application.rb file like so. Doing so would mean all generated assets will be in the a fresh css.less template.

config.app_generators.stylesheet_engine :less

We have generators for both assets and scaffold in the less namespace. For instance the following would generate a blank app/assets/stylesheets/posts.css.less template.

$ rails generate less:assets posts

We also have a generator for rails scaffold CSS. Just like the Sass gem, we simply parse the scaffold.css in the default rails generator and save it as a scaffolds.css.less file. This is done automatically during other scaffold generator actions.


Simply just run bundle install and bundle exec rake and the tests will will. We also use Travis CI to run our tests too. Current build status is:

Build Status


Less::Rails is Copyright (c) 2011 Ken Collins, and is distributed under the MIT license.

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