Personally, I've been using Haroopad as my long-form Markdown editor ( http://pad.haroopress.com/ http://pad.haroopress.com/ ). Good side-by-side preview, and

Personally, I've been using Haroopad as my long-form Markdown editor ( http://pad.haroopress.com/ http://pad.haroopress.com/ ). Good side-by-side preview, and I also run Hugo in server mode to double-check things. Haroopad sadly hasn't been updated in a couple years, but it works well enough for my purposes.