Why does it need a channel URL and not a video URL?
A video page's Open Graph image is the video's thumbnail, not the channel's avatar — there's no way to tell them apart from that field alone. This tool checks the URL shape and asks you to paste the channel page instead if it detects a video link.
Why did the download button open a new tab instead of saving the file?
YouTube's image CDN sometimes blocks direct cross-origin downloads from browser JavaScript. When that happens, this tool automatically falls back to an "open in new tab" link so you can still save the image with right-click → Save As.
Does this work for any public channel?
Yes, as long as the channel page is publicly accessible and YouTube serves a standard Open Graph image tag for it, which is true for essentially all public channels.
What resolution is the downloaded logo?
Whatever resolution YouTube publishes in its Open Graph tag for that channel — this tool doesn't upscale or modify the image in any way, it just retrieves it as-is.
Is any of this stored on your server?
No — the channel page is fetched on request, the image URL is extracted, and nothing about your lookup is stored afterward.