Markdown Previewer

About the Markdown Previewer

Markdown is a lightweight plain-text format that lets writers produce structured HTML without ever touching an angle bracket. It powers README files on GitHub, documentation sites, static-site generators, chat apps, and note-taking tools. This previewer takes the text you type, parses it into HTML in real time, and shows the rendered result side by side — so you see exactly how the published page will look while you write. Everything runs in your browser; no draft is ever uploaded.

How it works

The renderer targets CommonMark, the unambiguous specification of Markdown, layered with GitHub-Flavored Markdown (GFM) extras. The parser first tokenizes block-level constructs: headings (#, ##), ordered and unordered lists (1., -), fenced code blocks (triple backticks), blockquotes (>), thematic breaks, and paragraphs. It then resolves inline constructs inside each block: bold (**text**), italics (*text*), links ([text](url)), and inline code (single backticks). Each token becomes a corresponding HTML element, so Markdown is fundamentally a compiler from shorthand text to HTML.

GFM adds constructs that plain CommonMark lacks: pipe tables, task lists with [ ] / [x] checkboxes, and strikethrough with ~~text~~. Because the output is HTML that will live in a page, the rendered string is sanitized before insertion: raw <script> tags, inline event handlers such as onclick, and javascript: URLs are stripped. That sanitization is what prevents stored cross-site scripting (XSS) when user-authored Markdown is displayed — the single most important security property of any Markdown renderer.

Common use cases

• Drafting a project README and previewing it before pushing to GitHub
• Writing documentation that will be published as static HTML
• Checking that tables, task lists, and code fences render correctly
• Grabbing clean HTML to paste into a CMS or email template
• Reviewing GFM-specific syntax that plain Markdown parsers miss

Worked example

Given this Markdown snippet:

# Release notes
- Added **dark mode**
- Fixed `login` redirect
> Ships in v2.0

The renderer compiles it to this HTML:

<h1>Release notes</h1>
<ul>
  <li>Added <strong>dark mode</strong></li>
  <li>Fixed <code>login</code> redirect</li>
</ul>
<blockquote>
  <p>Ships in v2.0</p>
</blockquote>

The heading, list, inline strong and code, and blockquote all map one-to-one from their Markdown shorthand.