How Markdown Parsers Actually Work Under the Hood

Markdown to HTML conversion looks simple until you try to build a parser. The original Markdown specification by John Gruber is a 3,500-word document with enough ambiguity to produce dozens of incompatible implementations. Understanding how parsers work helps you write markdown that renders consistently everywhere. The parsing pipeline Every markdown parser follows roughly the same architecture: Lexing/Tokenizing - Break the input into tokens (headings, paragraphs, code blocks, lists, etc.) Parsing - Build a tree structure from the tokens Rendering - Walk the tree and output HTML The simplest possible markdown-to-HTML converter for a single feature: function headingsToHtml(markdown) { return markdown.replace(/^(#{1,6})\s+(.+)$/gm, (match, hashes, text) => { const level = hashes.length; return `<h${level}>${text}</h${level}>`; }); } headingsToHtml("# Hello\n## World"); // "<h1>Hello</h1>\n<h2>World</h2>" This regex approach works for headings in is