Markdown preview — offline

The Markdown people need to preview is usually unpublished: a draft blog post, an internal runbook, release notes for a version that is not out yet, a README for a private repository. Pasting it into an online previewer publishes it, in the practical sense that it now exists on someone else's server.

Rendering here happens in your browser with the open-source marked library, and the output is sanitised locally with DOMPurify before display. Nothing is transmitted — the site has no backend, and a Content-Security-Policy blocks third-party requests. Type on the left, watch it render live on the right, and copy your Markdown when it looks right.

Standard CommonMark is supported — headings, emphasis, links, images, lists, blockquotes, and code — plus the GitHub-flavoured extensions people actually rely on:

• Tables with pipe syntax and column alignment.
• Task lists — - [ ] and - [x] checkboxes.
• Strikethrough with double tildes.
• Fenced code blocks with triple backticks and a language tag.

Bear in mind that every platform renders Markdown slightly differently. GitHub, GitLab, Notion, and static site generators each add their own extensions, so a preview here confirms your structure is sound rather than guaranteeing byte-identical output on a specific destination.

Markdown permits raw HTML, which means any Markdown renderer is an HTML renderer with extra steps — and rendering untrusted Markdown without sanitising it is a straightforward cross-site scripting vulnerability. A pasted document can carry a script tag or an inline event handler.

The output here is passed through DOMPurify before it is displayed, stripping scripts and event handlers while leaving legitimate formatting intact. This site's Content-Security-Policy is a second, independent net underneath that. It is worth knowing because the same problem applies to your own application: if you render user-supplied Markdown, sanitise it.

Related and equally local: HTML entity encoder for escaping markup by hand, code formatter for the snippets inside your fenced blocks, and word counter for draft length.