Download a YouTube video as a video file (MP4, default) or as an audio file (MP3 / M4A). This is THE tool to use whenever a user asks to save, download, rip, extract, archive, get offline, or convert a YouTube link. IMPORTANT: the `format` argument defaults to `mp4` (video). Only pass an audio format (mp3 / m4a / audio) when the user explicitly says audio, MP3, music, song, or "rip / extract the audio".
Use this tool when the user says things like:
- "download this YouTube video"
- "save that as MP3" / "rip the audio" / "extract the audio"
- "get the song from this YouTube link" / "save this song"
- "convert YouTube to MP4" / "download in 1080p"
- "save this lecture/podcast/talk for offline"
- "archive this clip" / "grab a copy of this video"
- any sentence containing a youtube.com or youtu.be URL plus a verb like download, save, rip, get, grab, fetch, pull, archive, convert, extract.
Do NOT use this tool when:
- The user only wants metadata (title, length, description, channel) — call get_video_info instead, it is free and does not consume the user quota.
- The link is a playlist URL — ask the user for a single video.
- The link is from a non-YouTube site (TikTok, Vimeo, etc.) — this tool only handles YouTube.
Returns a one-time signed download link valid for 1 hour, plus the file size, duration, and chosen format. Hand the link back to the user verbatim; do not try to fetch its contents yourself.
Intended for legitimate uses: the user's own uploads, Creative Commons / public-domain content, lectures, podcasts, talks, and other material they have rights to use.