For example, Spotify's TOS prohibits recording audio:
8. User Guidelines
Spotify respects intellectual property rights and expects you to do the same. This means, for example, that the following is not permitted: (a) Copying, reproducing, “ripping”, recording, or making available to the public any part of the Spotify Services or content delivered to you via the Spotify Services
There's a question asking exactly this: Program to download music from Spotify
We do not enforce agreements between third parties - and we shouldn't set that precedent.
You're free to downvote, comment, and refrain from answering, but it's unlikely that any moderation action will be taking based solely on a contract being broken. I'm not a lawyer, and I don't intend to become one.
Youtube prohibits downloading videos or converting them to mp3 AFAIK and youtube-dl is very popular software that does that. The OP could argue that he wants to use it on websites other than youtube and how to judge him?
Since you can never know the true intentions of someone, you have to help him, and if he gets in troubles, its his own fault. For instance it's great to learn how to write computer virus, as long as you don't infect other people. Knowledge is always good.
