Jekyll uses Kramdown to convert Markdown by default. Kramdown was written in pure Ruby. I love Ruby as a programming language. But I’m aware that the alternative solution written in C will be faster.

Change Kramdown to CommonMark in Jekyll

For Markdown conversion an alternative solution to Kramdown is CommonMark. Jekyll has a dedicated gem called jekyll-commonmark. This gem uses the cmark-gfm library implemented in C.

Add a gem jekyll-commonmark to the group :jekyll_plugins in Gemfile

gem 'jekyll-commonmark'

In my opinion, it’s better to use the source directly from GitHub.

gem 'jekyll-commonmark', github: 'jekyll/jekyll-commonmark'

The jekyll-commonmark gem on RubyGems is not up to date. And I noticed that this gem in version 1.3.1 incorrectly colors the source code syntax.

After adding to Gemfile, call bundle install. If the gem installation was successful, the configuration needs to be improved.

In the file _config.yml find key markdown. Change the value of this key from kramdown to CommonMark. Remember that the markdown key is not required. If this key is not present, it defaults to kramdown. In this case, create the key markdown with the value CommonMark to override the default value.

It’s a good practice to set up the gem itself. CommonMark has options and extensions.

Part of the configuration file _config.yml

markdown: CommonMark
commonmark:
  extensions:
    - autolink
    - strikethrough
    - table
    - tagfilter
    - tasklist
  options:
    - FOOTNOTES
    - GITHUB_PRE_LANG
    - SMART
    - STRIKETHROUGH_DOUBLE_TILDE
    - UNSAFE

This blog also uses this configuration.

CommonMark advantage

The first and indisputable advantage of CommonMark is of course the processing speed.

CommonMark disadvantage

However, I also see disadvantages. Using markdown with CommonMark, you cannot add HTML attributes such as id or class. Kramdown allowed the following markdown:

{:.commonmark-vs-kramdown}
**CommonMark** is faster than **Kramdown**.

Kramdown parsed the above code to the following HTML:

<p class="commonmark-vs-kramdown">
  <strong>CommonMark</strong> is faster than <strong>Kramdown</strong>.
</p>

Unfortunately CommonMark parses it like this:

<p>{:.commonmark-vs-kramdown}
<strong>CommonMark</strong> is faster than <strong>Kramdown</strong>.</p>

I can live with it and use HTML in problematic places. But surely attribute handling would be a big, positive change for CommonMark. Maybe in the future…

{:.commonmark-support-html-classes} This is my test for CommonMark on a living organism. If you don’t see the {:.commonmark-support-html-classes} text at the beginning of the paragraph, then CommonMark supports this functionality or I have given up I have changed the markdown parser.


Simple dictionary

Extensions

  • autolink - Automatically converts the URL to an anchor tag.
  • strikethrough - Provides strikethrough support.
  • table - Provides table conversion. Tables drawn with ASCII characters are converted to HTML tags.
  • tagfilter - Disables unsafe tags. Filters tags like: <iframe>, <noembed>, <noframes>, <plaintext>, <script>, <style>, <textarea>, <title>, <xmp>. These tags change the way HTML is interpreted. That’s why they are escapes. During conversion for filtered tags, < is converted to &lt;.
  • tasklist - Provides item list support. You can create lists of varying depths. The list can be numbered (using numbers: 1, 2, 3, etc.). Or an unnumbered list (using the characters: +, -, *, etc.).

Options

  • FOOTNOTES - Parse footnotes. Footnotes can be placed anywhere. It’s good practice to include footnotes at the end of the file.
  • GITHUB_PRE_LANG - This option sets the data-lang attribute on the <pre> tag. By default, the data-lang attribute is in the <code> tag.
  • SMART - Use smart punctuation. The smart option converts ASCII characters to typographic characters. Three dots ... (period) are converted to ellipses (…). Text in ‘single’ and “double” quotation marks have a starting and ending tag. Depending on the number of dashes, different characters are used. Single dash -, double dash –, triple dash —, quad dash ––.
  • STRIKETHROUGH_DOUBLE_TILDE - Strikethrough only with two tildes. This means that it is ~~stricked text~~ and it’s ~not stricked text~. Using a single tilde for strikethrough is deprecated and is not recommended. A single tilde should be used for subscript. Similar behavior with double tildes is in Redcarpet.
  • UNSAFE - Allows inserting plain HTML.

Options that I don’t use

Options available in the documentation. I haven’t tested them in detail.

  • FULL_INFO_STRING - Include full info strings of code blocks in separate attribute
  • HARDBREAKS - Treat \n as hardbreaks (by adding <br/>).
  • LIBERAL_HTML_TAG - Support liberal parsing of inline HTML tags.
  • NOBREAKS - Translate \n in the source to a single whitespace.
  • SOURCEPOS - Include source position in rendered HTML.
  • TABLE_PREFER_STYLE_ATTRIBUTES - Use style instead of align for table cells
  • VALIDATE_UTF8 - Replace illegal sequences with the replacement character U+FFFD.