Thumbnail Analyzer

What it checks

• Contrast — samples brightness across the image to estimate whether it reads as flat/washed-out or has a clear range of light and dark.
• Headline legibility (approximate) — looks for regions of sharp light-to-dark transitions, which often line up with bold text or strong shapes. It does not perform text recognition, so it can't tell whether any text is actually present, correctly spelled, or genuinely legible.
• Phone-size readability — renders the image at roughly the size it appears in the YouTube mobile app, so it's easier to eyeball whether it still reads at a glance.

This runs a handful of simplified pixel heuristics — it can't predict click-through rate, and it isn't a substitute for testing a thumbnail with real viewers.