That being one I used for a long time, considered near essential although I had not used it for awhile, but it now seems to be defunct: urlchecker.org It allowed you to list a bunch of potential download URLs, like so: Cyberhost-1 link (e.g., "whatever".nitroflare.html) Cyberhost-2 link Cyberhost-3 link etc., up to a substantial list of them and urlchecker would report back to you which links were still valid / active for download, vs. which were dead. A great timesaver, as opposed to testing each link one by one. I think at one time this search tool even had an available API. In searching for some alternative, so far I have not found anything like that which is good or viable.
It's not a matter of bookmarks, and in a majority of cases, one would need to be a subscriber of the relevant cyberhost services in order for this to be useful, although some things may be downloadable -- slowly -- as a free user. But these would typically be download links showing up in various blogs, and as such they have some limited duration before they would expire. That might be anywhere from a couple weeks to a couple years.