The legality of using a YouTube to MP3 converter depends on several factors, including the country you are in and the content you are downloading. In some countries, downloading copyrighted material without permission is illegal, which includes downloading audio from copyrighted YouTube videos. However, in other countries, there may be some legal exceptions that allow for personal or educational use of copyrighted material.
It is important to note that YouTube's terms of service prohibit users from downloading videos or audio from their platform, so using a YouTube to MP3 converter may also be a violation of their terms of service. Additionally, downloading copyrighted material without permission is considered piracy and can result in legal consequences, such as fines or imprisonment.