Yeah you’ve got the right idea!
The key words to look for are:
読切 for short story (one-shot)
ショートショート for very short story
連載 for serialized story
There will always be a blurb of some kind saying if something is a 読切 or ショートショート, like this:
and they’re also often/always highlighted in the table of contents as “特別読切” you’ll notice they’re all “特別”.
連載 will always have a chapter title, which will usually have a chapter number (I would have said always but I noticed one series didn’t show a number here - still had the chapter title though).
Other potentially helpful blurbs:
On the side of the page there’s always a scene-setting one at the start and a scene-ending one at the end, which may or may not be helpful to get a tiny bit of grounding as to what’s going on if it’s the middle of a serial.
There’s usually also a blurb around the author’s name explaining a little about their background (and/or just listing what tankobon of theirs are available), and that can confirm the type of story too like this one reiterates it’s a 読切
