This is general information, not legal advice. Laws differ by country, and a lawyer in your jurisdiction is the right person to ask about your specific situation.
Three separate questions
People usually collapse three different things into one. Does copyright let you make a copy? Do the platform’s terms of service permit it? And what do you then do with the copy? A download can be fine on the first and third and still breach the second, which is a contract matter between you and the platform rather than a criminal one.
Content you own
The clearest case. Your own uploads are your own work, and downloading your Reel, your Short or your client’s video back off a platform is ordinary file management. This is the single most common legitimate use of a downloader.
Public domain and open licences
Work whose copyright has expired, work released into the public domain, and work published under a Creative Commons or similar licence can generally be downloaded and often reused — within whatever the licence requires, which usually means attribution.
Permission
If a creator says yes, you have permission. Getting that in writing, even a message, is worth the thirty seconds it takes. For commercial use it is essential.
Personal viewing versus republishing
Downloading a clip to watch on a flight is treated very differently from re-uploading it to your own account or putting it in an ad. Copyright cares most about distribution. Private viewing sits in a grey area that many jurisdictions treat leniently; republishing rarely does.
What is clearly not OK
Bypassing access controls to reach private or paid content, stripping DRM, and re-uploading other people’s work as your own. Those are not grey areas anywhere, which is why this tool supports only public content and refuses DRM-protected media outright.
A practical rule
Ask yourself who made it and what you are about to do with it. Your own work, or work you have permission for, used privately or with credit — you are fine. Someone else’s work, republished as yours or sold — you are not, however you obtained the file.
Terms of service are not criminal law
People often assume that because YouTube’s terms discourage downloading, doing it is illegal. That conflates two different systems. Terms of service are a contract between you and a platform; breaking them typically risks your account, not prosecution. Copyright is law, and it is what actually governs whether making and sharing a copy is lawful. Both matter, but they carry very different consequences, and confusing them leads people either to worry about nothing or to ignore something that matters.
Where fair use and fair dealing fit
Many countries allow limited use of copyrighted material without permission for criticism, commentary, news reporting, teaching or research. In the United States this is fair use; the United Kingdom, Canada, Australia and others have narrower fair dealing rules. These doctrines are decided case by case and depend on how much you take, why you took it and whether your use competes with the original. They are a real defence, not a magic phrase — quoting fifteen seconds of a video inside a critical review sits very differently from re-uploading the whole thing with a comment on top.
Practical steps that keep you covered
Three habits cover most situations. Keep a note of where a file came from and why you believed you could use it — a link and a date is enough, and it is the difference between a misunderstanding and a dispute. Ask in writing when the use is public or commercial; a screenshot of "sure, go ahead" has settled more arguments than any legal theory. And when you are unsure and the stakes are real — an ad, a paid piece of work, anything at scale — pay for a licence or use stock. The cost of licensing is almost always lower than the cost of being wrong.