File extension: .md, .markdown Developed by: John Gruber Type of format: Open file format MIME: text/markdown Markdown is a lightweight markup language for creating formatted text using a plain-text editor. John Gruber created Markdown in 2004 as an easy-to-read markup language. Markdown is widely used for blogging, instant messaging, and large language models, and also used elsewhere in online forums, collaborative software, documentation pages, and readme files.