Thumbnail Tester & Previewer
A thumbnail that looks great at 1280×720 in your editor has to survive at 120 pixels next to autoplay and ads. Upload your design — or pull a video's current thumbnail — and see it at the sizes viewers actually meet it, before you publish.
Preview your thumbnail
Everything stays in your browser. Load a second design into slot B for a side-by-side A/B comparison.
Judge it at the size it will be judged
Almost nobody meets your thumbnail at full resolution. The surfaces that decide whether a video gets clicked render it small: Home grid card (desktop) at 320×180px, Suggested / sidebar row at 168×94px, Search result row at 246×138px, Mobile list row at 160×90px. At those sizes, three-word text beats sentences, one face beats five, and value contrast beats saturation. The tester puts your design into each of those slots with a real title, channel line, and duration badge around it, because a thumbnail is never judged in isolation — it competes inside a noisy page.
A/B without self-deception
When you compare two designs, keep everything else identical — same title, same metadata, same surfaces. That is exactly what slot B does. It will not tell you which design gets more clicks (only publishing does that), but it will show you immediately which one survives shrinking to 120 pixels, and that eliminates most bad candidates before they cost you a launch.
Why the mockups are generic on purpose
These previews are evocative of "a video platform" — neutral grays, no logo, no cloned iconography — because YouTube's interface and branding belong to YouTube. The pixel sizes, text truncation, and badge placement are what you need to evaluate a thumbnail, and none of that requires imitating anyone's trade dress. ThumbnailPro is not affiliated with YouTube or Google.
Frequently asked questions
Why do the mockups look like a video platform but not exactly like YouTube?
Deliberately. YouTube’s interface, logo, and exact iconography are YouTube’s property, so the previews use neutral, generic video-platform layouts at the same display sizes instead. What matters for judging a thumbnail — the pixel dimensions, the surrounding text, the duration badge covering a corner — is all there; the branding is not.
Are the preview sizes real?
They are honest current typicals: 320×180, 168×94, 246×138, 160×90 pixels for the grid, sidebar, search, and mobile surfaces. Platforms shuffle these by a few pixels with every redesign, so treat them as representative display sizes, not a specification.
What is the grayscale toggle for?
A contrast check. A thumbnail that still reads clearly with the color removed has strong value contrast — the property that keeps it legible at small sizes and for viewers with color-vision deficiencies. If your design turns to mush in grayscale, it relies on hue alone.
Why does my uploaded image get cropped in the previews?
The preview slots are 16:9, like real video surfaces. If your image is a different shape — 4:3, square, vertical — the mockups crop it the way a “cover” fit does, and the tool tells you what percentage of which axis is hidden. Export at 16:9 (1280×720 or larger) to avoid the crop.
Is my image uploaded to a server?
No. The file is read by JavaScript in your tab, displayed from a local object URL, and discarded when you close the page. Nothing you upload leaves your device.
Can I compare two designs?
Yes — load a second image into slot B and every mockup renders both designs side by side with the same title and metadata, so the only variable is the thumbnail itself.
Images are processed locally and never transmitted. The preview sizes and crop math come from the same tested module documented on the methodology page.