Markdown previewer

How to preview Markdown

1. Type or paste your Markdown into the editor on the left.
2. The rendered HTML preview updates in real time on the right.
3. Switch to preview-only mode on mobile using the tab toggle.
4. Click "Copy HTML" to get the rendered HTML output.

Common uses

• Writing and previewing README files, documentation, or blog posts in Markdown, with a word counter to track length
• Checking how Markdown renders before committing to a repository, then run a readability check on the final prose
• Converting Markdown to HTML for embedding in a CMS or web page, using HTML entity encoding to escape special characters safely

Technical specification

• Algorithm or formula: CommonMark parsing with GitHub Flavored Markdown extensions (tables, task lists, strikethrough) implemented in the marked library.
• Browser API or library: marked (~40 KB minified) for Markdown to HTML conversion, run in a bundled Web Worker served from this site, started with the page and reused between runs; native iframe with the sandbox attribute for safe preview.
• Input limits: No hard length cap. Each conversion runs in the worker and is stopped after 2 seconds. Ordinary documents of several hundred KB convert well within that; unusual input, such as thousands of unmatched _ or * characters, can reach the limit at a few tens of KB. Very deeply nested blockquotes or lists show an error instead of a preview.
• Output: Rendered HTML in a sandboxed iframe; copyable raw HTML string for export.
• Known limitations: No syntax highlighting for fenced code blocks. The preview is sanitized against an allowlist: raw HTML is reduced to basic formatting, links show their URL as a tooltip and cannot be followed, and only images embedded as data: URLs display. Copy HTML returns marked's output unsanitized. No custom Markdown extensions beyond GFM.

Frequently asked questions

What Markdown spec does the tool follow?

The tool uses the marked library, which follows CommonMark (the standard Markdown specification) with GitHub Flavored Markdown extensions for tables and task lists.

Is my text sent to a server?

All rendering runs in your browser using the marked library. Our servers are not involved at any point.

Can I export the HTML output?

Yes. Click "Copy HTML" to copy the rendered HTML to your clipboard, then paste it into any HTML editor or CMS.

Does the tool support syntax highlighting in code blocks?

Fenced code blocks render as preformatted blocks, and a language hint such as ```js is kept in the HTML as class="language-js" on the <code> element, ready for a syntax highlighter on your own page. The preview itself shows code without language-specific colours.