Markdown Previewer

What is Markdown?

Markdown is a lightweight markup language created by John Gruber and Aaron Swartz in 2004, designed to let writers produce formatted documents using plain-text syntax that reads naturally even before conversion to HTML. A single # becomes an <h1>, double asterisks wrap text in <strong> tags, and indented lines become code blocks -- all without touching angle brackets. That simplicity drove adoption across platforms that handle millions of documents daily: GitHub uses Markdown for READMEs, pull request descriptions, and issue comments; Stack Overflow renders answers in Markdown; Reddit, Discord, and Notion all rely on Markdown or Markdown-derived syntax for user content. Two dominant specifications exist today -- CommonMark, a strict unambiguous standard, and GitHub Flavored Markdown (GFM), which extends CommonMark with tables, task lists, strikethrough, and autolinked URLs. This previewer parses GFM client-side using the marked library, so your documents never leave your browser.

Common Use Cases for Markdown

The most visible use of Markdown is the README.md file found in virtually every open-source repository. It serves as the project's landing page on GitHub, GitLab, and Bitbucket, making first impressions for potential contributors. Beyond READMEs, Markdown powers entire documentation ecosystems: MkDocs, Docusaurus, and GitBook all compile Markdown files into polished documentation sites with search, versioning, and navigation. Static-site generators like Jekyll, Hugo, and Gatsby use Markdown as their primary content format, letting bloggers write posts without a CMS. Knowledge-management tools such as Obsidian store everything as interconnected .md files, creating a personal wiki that remains portable because the underlying format is plain text. API documentation written in Markdown can be embedded alongside OpenAPI specs or rendered inside developer portals. Presentation frameworks like Marp and reveal.js turn Markdown slides into browser-based decks, and Jupyter notebooks use Markdown cells to narrate data analysis between code blocks. Developers prefer Markdown over rich-text editors because files are diffable in version control, lightweight to store, and immune to the formatting corruption that plagues binary document formats. A Markdown file written in 2004 still renders perfectly today -- that longevity is unmatched by proprietary formats.

Markdown Syntax Essentials

Headings use one to six # symbols (# H1 through ###### H6), creating a semantic document outline that screen readers and search engines can parse. Emphasis is applied with asterisks: *italic* and **bold**, which can be nested as ***bold italic***. Links follow [text](url) syntax, while images prepend an exclamation mark: ![alt](src). Inline code uses single backticks, and fenced code blocks use triple backticks with an optional language identifier for syntax highlighting -- for example, ```javascript triggers JS-specific color coding in most renderers. Unordered lists use -, *, or + as bullet markers; ordered lists use numbers followed by a period. Blockquotes are prefixed with > and can be nested. Tables are drawn with pipes and hyphens, aligning columns visually in the source. GFM extends standard Markdown with ~~strikethrough~~, task lists (- [x] done / - [ ] pending), automatic URL linking, and footnote support. Horizontal rules (---) divide long documents into scannable sections. Mastering these elements covers roughly 95% of day-to-day Markdown writing.