1. 01Choose HTML→Markdown or Markdown→HTML.
2. 02Paste your text, or import a .html/.htm/.md/.markdown/.txt file; a manual file import must not exceed 10 MiB.
3. 03Wait for the roughly 250ms debounced conversion, then inspect the output and the optional safe preview.
4. 04Copy the result, or download converted.md / converted.html.

• HTML→Markdown targets semantic body copy; complex tables, nested layouts or structures that lean on CSS may degrade to simple Markdown or plain text.
• Markdown→HTML uses GFM, but the editor page's breaks: true option is not enabled here; a single ordinary line break can therefore behave differently from the editor preview.
• Manual file imports are capped at 10 MiB; the read path that relays files through the site's transfer feature does not repeat this size check inside this component.
• Files are read as text through the browser's File.text(); this is not a binary HTML/Markdown converter, so bytes in the wrong encoding may first be replaced by the browser's text decoding.
• DOMPurify deletes scripts and dangerous attributes, so a round trip through unsafe HTML is not guaranteed to come back word for word.

Input files and text are read, parsed and converted locally in your browser and are never uploaded; what is loaded dynamically is the site's conversion library code, which does not send your prose out as an external request.