Kramdown

Kramdown is a fast, pure Ruby Markdown parser and converter. It provides a Markdown syntax that is a superset of common Markdown features and also offers compatibility modes for GitHub Flavored Markdown (GFM). The project is designed to be fast and extensible for Ruby applications and is widely used, notably as the default Markdown processor in the Jekyll static site generator.

Kramdown supports a broad range of features commonly used in Markdown documents, including tables, fenced code blocks, footnotes, and definition lists. It also provides block and inline attributes that let authors assign IDs, classes, and other metadata to elements. In addition, it offers built-in support for math notation with engines such as MathJax, KaTeX, or MathML, and supports GitHub Flavored Markdown mode for compatibility with non-kramdown syntax.

Internally, kramdown parses input into a document tree and renders output through a configurable writer system. It can produce HTML by default, and can also output XHTML, LaTeX, or other formats depending on the selected writer and options.

In Ruby projects, kramdown is used by invoking the Kramdown::Document with the markdown text and converting it to_html or to other formats; in Jekyll, it functions as the default Markdown processor.

Kramdown is released under the MIT License and is available as a Ruby gem.