Markdown

John Gruber created Markdown in 2004, with Aaron Swartz, so that text would stay readable before any conversion. The original description left many edge cases open, so CommonMark defined a precise specification in 2014, and GitHub Flavored Markdown adds tables, task lists, strikethrough and automatic links on top. Front matter, a YAML block at the top of a file, is a common add-on for titles, dates and tags.

It is used for READMEs, documentation, blogs, notes apps, chat messages and the output of AI models. Libraries such as marked, markdown-it, remark and react-markdown turn it into HTML. Because Markdown allows raw HTML, anything written by untrusted users should be sanitised after conversion to prevent XSS. MDX extends it with components.