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Plugins

Jekyll has a plugin system with hooks that allow you to create custom generated content specific to your site. You can run custom code for your site without having to modify the Jekyll source itself.

Plugins on GitHub Pages

GitHub Pages is powered by Jekyll, however all Pages sites are generated using the --safe option to disable custom plugins for security reasons. Unfortunately, this means your plugins won’t work if you’re deploying to GitHub Pages.

You can still use GitHub Pages to publish your site, but you’ll need to convert the site locally and push the generated static files to your GitHub repository instead of the Jekyll source files.

Installing a plugin

You have 2 options for installing plugins:

  1. In your site source root, make a _plugins directory. Place your plugins here. Any file ending in *.rb inside this directory will be loaded before Jekyll generates your site.
  2. In your _config.yml file, add a new array with the key gems and the values of the gem names of the plugins you’d like to use. An example:
    gems: [jekyll-test-plugin, jekyll-jsonify, jekyll-assets]
    # This will require each of these gems automatically.
_plugins and gems can be used simultaneously

You may use both of the aforementioned plugin options simultaneously in the same site if you so choose. Use of one does not restrict the use of the other

In general, plugins you make will fall into one of three categories:

  1. Generators
  2. Converters
  3. Tags

Generators

You can create a generator when you need Jekyll to create additional content based on your own rules.

A generator is a subclass of Jekyll::Generator that defines a generate method, which receives an instance of Jekyll::Site.

Generation is triggered for its side-effects, the return value of generate is ignored. Jekyll does not assume any particular side-effect to happen, it just runs the method.

Generators run after Jekyll has made an inventory of the existing content, and before the site is generated. Pages with YAML Front Matters are stored as instances of Jekyll::Page and are available via site.pages. Static files become instances of Jekyll::StaticFile and are available via site.static_files. See the Variables documentation page and Jekyll::Site for more details.

For instance, a generator can inject values computed at build time for template variables. In the following example the template reading.html has two variables ongoing and done that we fill in the generator:

module Reading
  class Generator < Jekyll::Generator
    def generate(site)
      ongoing, done = Book.all.partition(&:ongoing?)

      reading = site.pages.detect {|page| page.name == 'reading.html'}
      reading.data['ongoing'] = ongoing
      reading.data['done'] = done
    end
  end
end

This is a more complex generator that generates new pages:

module Jekyll

  class CategoryPage < Page
    def initialize(site, base, dir, category)
      @site = site
      @base = base
      @dir = dir
      @name = 'index.html'

      self.process(@name)
      self.read_yaml(File.join(base, '_layouts'), 'category_index.html')
      self.data['category'] = category

      category_title_prefix = site.config['category_title_prefix'] || 'Category: '
      self.data['title'] = "#{category_title_prefix}#{category}"
    end
  end

  class CategoryPageGenerator < Generator
    safe true

    def generate(site)
      if site.layouts.key? 'category_index'
        dir = site.config['category_dir'] || 'categories'
        site.categories.keys.each do |category|
          site.pages << CategoryPage.new(site, site.source, File.join(dir, category), category)
        end
      end
    end
  end

end

In this example, our generator will create a series of files under the categories directory for each category, listing the posts in each category using the category_index.html layout.

Generators are only required to implement one method:

Method Description

generate

Generates content as a side-effect.

Converters

If you have a new markup language you’d like to use with your site, you can include it by implementing your own converter. Both the Markdown and Textile markup languages are implemented using this method.

Remember your YAML Front Matter

Jekyll will only convert files that have a YAML header at the top, even for converters you add using a plugin.

Below is a converter that will take all posts ending in .upcase and process them using the UpcaseConverter:

module Jekyll
  class UpcaseConverter < Converter
    safe true
    priority :low

    def matches(ext)
      ext =~ /^\.upcase$/i
    end

    def output_ext(ext)
      ".html"
    end

    def convert(content)
      content.upcase
    end
  end
end

Converters should implement at a minimum 3 methods:

Method Description

matches

Does the given extension match this converter’s list of acceptable extensions? Takes one argument: the file’s extension (including the dot). Must return true if it matches, false otherwise.

output_ext

The extension to be given to the output file (including the dot). Usually this will be ".html".

convert

Logic to do the content conversion. Takes one argument: the raw content of the file (without YAML Front Matter). Must return a String.

In our example, UpcaseConverter#matches checks if our filename extension is .upcase, and will render using the converter if it is. It will call UpcaseConverter#convert to process the content. In our simple converter we’re simply uppercasing the entire content string. Finally, when it saves the page, it will do so with a .html extension.

Tags

If you’d like to include custom liquid tags in your site, you can do so by hooking into the tagging system. Built-in examples added by Jekyll include the highlight and include tags. Below is an example of a custom liquid tag that will output the time the page was rendered:

module Jekyll
  class RenderTimeTag < Liquid::Tag

    def initialize(tag_name, text, tokens)
      super
      @text = text
    end

    def render(context)
      "#{@text} #{Time.now}"
    end
  end
end

Liquid::Template.register_tag('render_time', Jekyll::RenderTimeTag)

At a minimum, liquid tags must implement:

Method Description

render

Outputs the content of the tag.

You must also register the custom tag with the Liquid template engine as follows:

Liquid::Template.register_tag('render_time', Jekyll::RenderTimeTag)

In the example above, we can place the following tag anywhere in one of our pages:

<p>{% render_time page rendered at: %}</p>

And we would get something like this on the page:

<p>page rendered at: Tue June 22 23:38:47 –0500 2010</p>

Liquid filters

You can add your own filters to the Liquid template system much like you can add tags above. Filters are simply modules that export their methods to liquid. All methods will have to take at least one parameter which represents the input of the filter. The return value will be the output of the filter.

module Jekyll
  module AssetFilter
    def asset_url(input)
      "http://www.example.com/#{input}?#{Time.now.to_i}"
    end
  end
end

Liquid::Template.register_filter(Jekyll::AssetFilter)
ProTip™: Access the site object using Liquid

Jekyll lets you access the site object through the context.registers feature of Liquid at context.registers[:site]. For example, you can access the global configuration file _config.yml using context.registers[:site].config.

Flags

There are two flags to be aware of when writing a plugin:

Flag Description

safe

A boolean flag that informs Jekyll whether this plugin may be safely executed in an environment where arbitrary code execution is not allowed. This is used by GitHub Pages to determine which core plugins may be used, and which are unsafe to run. If your plugin does not allow for arbitrary code, execution, set this to true. GitHub Pages still won’t load your plugin, but if you submit it for inclusion in core, it’s best for this to be correct!

priority

This flag determines what order the plugin is loaded in. Valid values are: :lowest, :low, :normal, :high, and :highest. Highest priority matches are applied first, lowest priority are applied last.

To use one of the example plugins above as an illustration, here is how you’d specify these two flags:

module Jekyll
  class UpcaseConverter < Converter
    safe true
    priority :low
    ...
  end
end

Available Plugins

You can find a few useful plugins at the following locations:

Generators

Converters

Filters

  • Truncate HTML by Matt Hall: A Jekyll filter that truncates HTML while preserving markup structure.
  • Domain Name Filter by Lawrence Woodman: Filters the input text so that just the domain name is left.
  • Summarize Filter by Mathieu Arnold: Remove markup after a <div id="extended"> tag.
  • i18n_filter: Liquid filter to use I18n localization.
  • Smilify by SaswatPadhi: Convert text emoticons in your content to themeable smiley pics.
  • Read in X Minutes by zachleat: Estimates the reading time of a string (for blog post content).
  • Jekyll-timeago: Converts a time value to the time ago in words.
  • pluralize: Easily combine a number and a word into a gramatically-correct amount like “1 minute” or “2 minutes”.
  • reading_time: Count words and estimate reading time for a piece of text, ignoring HTML elements that are unlikely to contain running text.
  • Table of Content Generator: Generate the HTML code containing a table of content (TOC), the TOC can be customized in many way, for example you can decide which pages can be without TOC.
  • jekyll-humanize: This is a port of the Django app humanize which adds a “human touch” to data. Each method represents a Fluid type filter that can be used in your Jekyll site templates. Given that Jekyll produces static sites, some of the original methods do not make logical sense to port (e.g. naturaltime).
  • Jekyll-Ordinal: Jekyll liquid filter to output a date ordinal such as “st”, “nd”, “rd”, or “th”.
  • Deprecated articles keeper by Kazuya Kobayashi: A simple Jekyll filter which monitor how old an article is.

Tags

Collections

Other

Editors

  • sublime-jekyll: A Sublime Text package for Jekyll static sites. This package should help creating Jekyll sites and posts easier by providing access to key template tags and filters, as well as common completions and a current date/datetime command (for dating posts). You can install this package manually via GitHub, or via Package Control.
  • vim-jekyll: A vim plugin to generate new posts and run jekyll build all without leaving vim.
Jekyll Plugins Wanted

If you have a Jekyll plugin that you would like to see added to this list, you should read the contributing page to find out how to make that happen.