markdown-it

markdown-it is a highly extensible and standards-compliant Markdown parser written in JavaScript, designed to provide fast, pluggable, and CommonMark-specification-conformant parsing of Markdown text into HTML. Created by Vitaly Puzrin and the Marker.js team, it has become one of the most popular Markdown parsing libraries in the Node.js and browser ecosystems, widely used in documentation generators, static site generators, wikis, content management systems, and developer tools. The library follows the CommonMark specification strictly by default, ensuring consistent and predictable rendering across different platforms. Beyond standard CommonMark, markdown-it supports GitHub Flavored Markdown extensions through optional plugins, including tables, strikethrough, task lists, and autolinks. The architecture is built around a two-phase parsing approach: the Parse phase converts Markdown source into a token stream (an intermediate representation that is easy to manipulate), and the Render phase converts the token stream into HTML output. This design allows developers to insert custom rules at any point in the parsing pipeline, enabling fine-grained control over how specific Markdown constructs are processed. Key features include: pluggable architecture with a rich ecosystem of community plugins (over 200 available), syntax highlighting integration (via highlight.js or Prism), typographic replacements (smart quotes, dashes, ellipses), HTML sanitization options, link validation and normalization, attribute customization for HTML elements, and configurable line numbering for source mapping. The library has zero runtime dependencies, ships as a single file, and supports both synchronous and streaming APIs. With over 18,000 GitHub stars and over 30 million weekly npm downloads, markdown-it is trusted by VuePress, Docusaurus, GitLab, and many other major projects.