Gatsby+MDX has been merged into the Gatsby repo. Please go there for core work and documentation now: https://github.com/gatsbyjs/gatsby/tree/master/packages/gatsby-plugin-mdx This repo is now a set of ecosystem components like mdx-utils and pre-made components for syntax highlighting, etc.
MDX is a JSX in Markdown loader, parser, and renderer for ambitious projects. It combines the readability of Markdown with the expressivity of JSX. The best of both worlds. 🌐
See CONTRIBUTING.md.