Glance test for thumbnails
Video Thumbnail Tester
Upload a thumbnail and check whether the subject still reads when small or slightly blurred. Catch weak titles and busy frames before you publish.
Quick answer
Video Thumbnail Tester is a free browser tool on Knowlify. Use it below with no signup. Your inputs stay in the browser session. For narrated training videos from documents, use https://create.knowlify.com.
How it works
Three steps, no account
01
Upload a thumbnail
PNG or JPG works. Use the exact export you plan to publish.
02
Run the glance tests
View small, medium, and blurred versions. If the subject disappears, simplify.
03
Iterate
Crop tighter, increase contrast, reduce text. Then ship the video or generate a new one in Knowlify.
FAQ
Questions people ask about Video Thumbnail Tester
What makes a strong thumbnail?+
One clear subject, high contrast, minimal text, and a composition that survives being tiny on mobile.
Is the thumbnail tester free?+
Yes. Preview how a thumbnail looks at feed sizes with no signup.
How do I test a YouTube thumbnail?+
Upload the image and review small sizes. Check contrast, subject clarity, and whether text is still readable.
Can I download YouTube thumbnails from other videos?+
Yes. Use the YouTube thumbnail downloader for research, then redesign and test your own image here.
Do I need an account?+
No. Open the tool, use it in your browser, and download or copy the result.
Does this work on Mac and Windows?+
Yes. It runs in modern desktop browsers (Chrome, Edge, Firefox, Safari). Very large media files need enough device memory.
Need a full video, not just a utility?
Thumbnail fixed? Make sure the video behind it is just as clear. Generate explainers and training videos with Knowlify.