YouTube has become one of the most popular online platforms for music streaming and video sharing. However, the lack of a built-in download feature has led to the development of third-party YouTube downloaders. This paper presents the design and implementation of a YouTube downloader with a serial key, specifically focusing on YouTube Music Downloader. The proposed system allows users to download YouTube music videos in various formats, including MP3, MP4, and more. The system utilizes a serial key for user authentication and authorization, ensuring secure and controlled access to the download feature.