Fetching and measuring…
The thumbnail
How it looks where people actually see it
360px · desktop grid
246px · mobile feed
168px · sidebar
Every tool makes thumbnails. This one grades them.
Paste a YouTube link and the thumbnail gets pulled and measured: does it survive being shrunk to feed size, is the contrast strong enough, does the duration badge sit on top of something that mattered. Measured facts about the image, not a made-up click-through score.
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Plenty of tools will give a thumbnail a score out of 100 and a predicted click-through rate. Those numbers are invented. Click-through depends on your title, your audience, the topic, what else is on the page and when it was posted. No tool looking at a single image can know any of that, and one that claims otherwise is selling confidence rather than information.
So this page reports only what can actually be measured from the pixels, and names the threshold it is comparing against in every case. What you do with that is your call.
| Check | How it is measured |
|---|---|
| Dimensions and aspect | Compared against YouTube's 1280 by 720 recommendation and 16:9. Anything else gets letterboxed or cropped somewhere. |
| Feed-size detail | The image is rendered down to 168 by 94, the sidebar size, and the mean absolute Laplacian is computed on it. That is a standard edge-energy measure: it falls when shapes and text turn into mush at small scale. |
| Global contrast | Standard deviation of luminance across the whole image, on a 0 to 100 scale. Low values mean a flat image that recedes in a busy feed. |
| Duration badge collision | YouTube stamps a timestamp over the bottom-right corner. That region is checked for edge density; a high value means something detailed is about to be covered up. |
| Edge margins | The outer 4 percent is checked for detail, because different surfaces crop thumbnails slightly differently and content parked at the very edge is the first thing to be lost. |
| Tonal range | The share of pixels that are nearly black or nearly white. Large amounts of either mean detail is already clipped and will not survive further compression. |
A thumbnail is designed at 1280 by 720 and almost never seen at 1280 by 720. In a desktop sidebar it renders around 168 pixels wide. On a phone it is a little larger but sits further from the eye. The practical effect is the same: roughly a seventh of the linear detail you were looking at while designing it.
This is why the usual advice about thumbnails is what it is. Three or four words maximum, because more will not be read. Heavy type, because thin strokes vanish. One clear subject, because a busy composition becomes texture. None of that is style preference; it is a consequence of the display size.
The three renders above are the actual sizes. Look at the 168 pixel one and ask whether you can tell what the video is about. That single question is worth more than any score.
Keep going without re-uploading — your image carries over to the next tool automatically.