@robi Yes Musicbrainz and others do this well today, if your song match an existing hash you get a beautifully tagged library in no time, provided it's mainstream CDdb & other sources based, the link above mentions these possibilities.
Ampache can also do some of this, it has a bunch of API spots to fill for different services, spotify among them, to do just that if you also enabled iD3 rewriting based on what it gets from different sources.
I'm not using any of that but for example, just by activating some of the plugins to fetch artist data from different places, some of my mixes got a nice cover they did not have before, so this is working, even for mixes that have 2 decades already 🙂