Transit is covered by a short-stay visa; VFS also lists a separate type B (transit) category in some countries, so choose the category together with the centre. The 30-day rule above explicitly includes transit, so a valid Schengen, US, UK or Irish visa also covers passing through Montenegro. For visa-required travellers without such a document, transit through Montenegro needs a visa too, unless a published rule says otherwise.
The reverse question comes up just as often. A Montenegrin visa or entry stamp gives no right to enter the Schengen area. If your route runs through Vienna, Rome or another Schengen hub, you need whatever Schengen entry your passport requires, separately. Our guide to
flights to Montenegro explains the main routes and why multi-stop itineraries need careful planning.