Jonathon Kram has informed me that Kramdown does, indeed, support Footnotes. Using it is likely easier than the method I describe in this post. Thanks, Jonathon!
1) Use the fork
The RedCarpet gem we want to use is not available on RubyGems.org, but Bundler can install it directly from GitHub. Add a
Gemfile to your Jekyll site’s root directory that looks like this:
source "https://rubygems.org" gem "jekyll" gem "redcarpet", github: "triplecanopy/redcarpet"
bundle install and then you should be all ready to go.2
2) Configure RedCarpet
You have to configure Jekyll to use RedCarpet for Markdown rendering, but you also have to configure RedCarpet to use the
footnotes extension. Add these lines to your
markdown: redcarpet redcarpet: extensions: [footnotes]
That’s it! You now have footnotes with Jekyll.
Footnotes is not an official Markdown feature, but was added by PHP-Markdown and a few derivative projects. The feature hasn’t made it in to RedCarpet proper (by way of Sundown) because of the concerted effort by GitHub, Reddit, etc. to develop and support a Markdown standard which will replace Sundown. See this issue if you’re interested in learning more. ↩