GitLab Kramdown

This is an official gem that implements GitLab flavored Markdown extensions on top of Kramdown.

Note: This is not the same code that runs on GitLab. The GitLab flavored Markdown runs on top of CommonMark with extensions implemented inside the Rails application.

GitLab Flavored Markdown extensions support

This is a list of GitLab Flavored Markdown (GLFM) extensions and their status of support on this gem:

GLFM Extensions	Implemented?
Newlines	No
Multiple underscores in words	Kramdown
Headers with Anchors	Yes
URL auto-linking	Yes
Multiline Blockquote	Yes
Code and Syntax Highlighting	Yes
Strikethrough	Yes
Inline Diff	No
Emoji	No
Special GitLab references	Yes
Task Lists	No
Videos	No
Math	No
Colors	No
Mermaid	Yes
PlantUML	Yes
[JSON Table]	No

Note: Extensions marked as Kramdown in the Implemented? means behavior already exists in Kramdown flavor.

Configuration parameters

Parameter	Default	Description
`gitlab_url`	`https://gitlab.com`	GitLab instance URL to build reference links
`linkable_headers`	true	Generate anchor tags with headers?
`autolink`	false	Converts URLs to HTML links (can be slow)
`clickable_images`	true	Autolink images to themselves

Usage example

To use this gem you're also required to install Kramdown. This gem will hook into Kramdown and provide custom parser.

require 'kramdown'
require 'gitlab_kramdown'

source = <<-EOF
# GLFM example

We support custom extensions like:

>>>
This is a multiline
Blockquote

Using `>>>` as delimiter
>>>
EOF

Kramdown::Document.new(source, input: 'GitlabKramdown').to_html

To have also syntax highlighting using the same engine GitLab use, you need to define the highlighter as :rouge:

Kramdown::Document.new(source, input: 'GitlabKramdown', syntax_highlighter: :rouge).to_html

Supported and tested Ruby versions

Ruby 3.0
Ruby 3.2

Release a new version

To release a new version of GitLab Kramdown:

Update the CHANGELOG.md file for the new version.
Check lib/gitlab_kramdown/version.rb is updated for the new version.
Commit changes to a new branch.
Run rake release.

Contributing to gitlab_kramdown

Check out the main branch to make sure the feature hasn't been implemented or the bug hasn't been fixed yet.
Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it.
Fork the project.
Start a feature/bugfix branch.
Commit and push until you are happy with your contribution.
Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.