The browser is the right answer most of the time. This page is about the cases where it structurally cannot be.
A hosted downloader receives a URL, fetches it, and returns a file. It arrives as an anonymous visitor: no session cookie, no account, no purchase history, no access grant. If the page serves its media only to a signed-in user, the fetch fails — not because the tool is weak, but because the request was never entitled to the bytes.
That boundary is a feature. The alternative would be handing your session to a third party, which is a much worse trade than running a program locally.
The Keep Video desktop app is the local half of the same project, packaged for macOS, Windows and Linux. For single public links the browser version is still faster — no install, no account.
A rough rule that holds up in practice:
Both produce the same kind of artefact, so the naming and indexing habits from the field guide apply either way. And in both cases the permission question is unchanged: save what you own or are licensed to keep.