Show HN: Free AI Thumbnail Tester (based on real YouTube data) (aithumbnail.so)

I built this free tool to analyze YouTube thumbnails using a proven checklist I first found on Reddit. It grades clarity, contrast, text readability, and visual hierarchy, all using AI.

It's now live on aithumbnail.so. I believe it’s one of the most accurate tools out there for thumbnail testing.

Would love feedback, ideas, or bug reports!