See your thumbnail in the feed before you publish.
Thumbnail Tester is a browser-based tool for previewing one YouTube thumbnail and one video title in simulated desktop and phone feed layouts. Add an image and title, switch views, and save the current layout as a PNG; the image stays in this browser.
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What can you check before publishing?
What does Thumbnail Tester check?
It shows one thumbnail and one video title in simulated desktop and phone feed layouts so you can check the composition before publishing.
Does the image leave your device?
No. The preview and export run in this browser, and the selected image is not uploaded to the site.
Can you save the preview?
Yes. Use Save current view to export the visible desktop or phone preview as a PNG.
What sources support this tool?
SOURCE The preview is a local layout mockup. The thumbnail guidance on this site is cross-checked against YouTube Studio Help and YouTube Help.
"For videos, try to upload a thumbnail with an aspect ratio of 16:9."
— YouTube Studio Help, Add custom thumbnails on YouTube
MAINTAINED Maintained by Feed Thumbnail. Last updated September 14, 2026.