Translating, checking a spec, rewriting an old version into a new one — all of those mean reading A while writing B. Browser tabs can't sit side by side, and lining up two windows by hand gets old fast. So the editor carries a second preview.
The Side-by-side dual preview button splits the preview area in half:
The right half has two buttons:
| Button | What it does |
|---|---|
| 📂 Load MD | pick any .md to display on the right |
| 📁 Authorize folder | set a base folder so the right half can show full relative paths instead of bare file names |
You can also drop a file onto the right half and it lands there; drop it on the left half and it becomes the file you are editing. Whichever side of the midline your cursor is on is where the file goes.
Above the right half there is a Sync scroll checkbox. With it on, both sides move proportionally: scroll one pane to 40 % and the other goes to its own 40 %.
It deliberately does not try to align line by line. Two documents almost never share line counts or paragraph heights, so forcing that would make the panes jump around while you scroll. Proportional scrolling is the more predictable behaviour.
Uncheck it and each side scrolls on its own again.
Turn off Show / hide editor and only the previews remain. Combined with dual preview, that is two documents side by side with no editing field taking up space. Turn it back on and your text and scroll position are still there.
The sidebar can be collapsed too, for the widest possible reading area. Both toggles are remembered in your browser, so the next visit looks the way you left it.
Press Side-by-side dual preview again (or the close button on the right half) to return to a single preview. Whatever you loaded on the right never affects the file you are editing — it is read-only reference material from beginning to end.
Download this page as .md Open it in the editor and you have a ready-made sample document.