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Markup

Markdown to HTML Viewer

Import, paste, or type Markdown, convert it with Marked in GFM mode, sanitize the HTML with DOMPurify, preview it, and copy the allowed markup locally. Useful for writers, documentation authors, and developers previewing Markdown rendering with GitHub-flavored extensions.

Markdown tools

In brief

Marked parses GFM Markdown and one audited DOMPurify policy removes scripts, forms, images, styles, SVG, embeds, and unsafe URLs before preview or copy.

What this tool supports

  • Reads typed, pasted, .md, or .markdown text and parses it with Marked using GFM mode and normal soft-line behavior.
  • Preserves allowed HTML such as headings, paragraphs, emphasis, lists, blockquotes, code, tables, and safe links after DOMPurify sanitization.
  • Removes script, style, iframe, form controls, images, SVG/MathML, embeds, metadata, inline style, srcset, and unsafe URI schemes.
  • Renders a live or manual preview, forces retained links into a new tab with noopener/noreferrer, and copies the sanitized HTML string.

How to use Markdown to HTML Viewer

Follow this implementation-specific workflow for Sanitized Markdown-to-HTML Viewer; each step reflects the controls and limits in the current browser workspace.

  1. 1

    Step 1

    Provide the exact source

    Type or paste Markdown, import a .md/.markdown file, or load the supplied sample.

  2. 2

    Step 2

    Choose the operation

    Keep Live enabled for immediate conversion or turn it off while editing and press Render when ready.

  3. 3

    Step 3

    Configure the available options

    Let Marked parse GFM syntax and DOMPurify apply the project’s restrictive Markdown policy.

  4. 4

    Step 4

    Run the local operation

    Inspect the preview and character count, especially links, tables, code fences, and any raw HTML that may have been removed.

  5. 5

    Step 5

    Verify and continue

    Copy the sanitized HTML and test it again inside the destination’s own sanitizer and stylesheet.

Common mistakes

Expecting embedded images or raw forms to appear

Consequence: The security policy deliberately forbids img, form, input, button, iframe, SVG, MathML, style, and related active or network-capable markup.

Fix: Host approved assets separately and add them only in a destination with its own reviewed content-security policy.

Assuming the preview’s appearance is part of copied HTML

Consequence: Typography comes from the application’s prose CSS; the copied string contains markup, not those styles.

Fix: Preview the copied HTML under the destination stylesheet before publishing.

Treating sanitization here as permanent protection everywhere

Consequence: A destination may transform, concatenate, or re-sanitize markup under a different policy.

Fix: Keep sanitization at the final trust boundary and use this output only as an intermediate reviewed artifact.

Best practices

  • Keep raw Markdown as the editable source and regenerate HTML instead of editing copied markup by hand.
  • Review every outbound link; the viewer adds rel protection but does not vouch for the linked site.
  • Test headings, lists, tables, and code in the final renderer because Markdown dialect and CSS differences affect presentation.

Connected workflows

Browser limitations

  • This is Marked GFM behavior, not a byte-for-byte CommonMark conformance oracle; extensions and raw-HTML handling can differ in another renderer.
  • Images and active/network-capable elements are removed by design, and there is no syntax-highlighting, export-file, template, or custom sanitizer option.
  • Parsing and DOM sanitization run synchronously on the main thread, so very large documents can pause editing and preview.

Authoritative resources

CommonMark Specification 0.31.2Publisher: CommonMark · Reviewed: 2026-07-26Marked documentation and security guidancePublisher: Marked project · Reviewed: 2026-07-26DOMPurify security documentationPublisher: Cure53 · Reviewed: 2026-07-26

Concrete examples

Input
# Release Notes **Ready** for review.
Result
A heading and paragraph are previewed, and the same sanitized HTML can be copied.

Marked emits the two elements and DOMPurify keeps these allowed tags because they contain no forbidden attributes or URL schemes.

Frequently asked questions

Why did an image in my Markdown disappear?

The shared policy forbids img entirely to prevent unintended network requests and unsafe embedded content in this preview.

Are raw HTML tags accepted inside Markdown?

Marked can parse raw HTML, but DOMPurify then removes forbidden tags/attributes and retains only the configured safe HTML profile.

What happens to Markdown links?

Allowed http, https, mailto, relative, root, and fragment targets survive; every resulting anchor receives target=_blank and rel=noopener noreferrer.

Can I copy the CSS used by the preview?

No. Copy returns only the sanitized HTML string; the application’s prose classes and theme styles are not embedded.

Is this suitable for rendering untrusted Markdown in production?

It demonstrates the project’s audited browser policy, but a production system still needs sanitization at its own final trust boundary, CSP, dependency updates, and regression tests.

Privacy and offline behavior

Markdown source and sanitized HTML stay in the current browser. Imported files are read as text only after selection, and conversion works offline after app assets are cached; clipboard copying is the only intentional data handoff.