YouTube Thumbnail Tester by Ramboozled

See how your next video could look among the videos on your desktop YouTube homepage.

Click the extension button to open the tester on YouTube Home. If you are elsewhere, it opens or reuses a YouTube homepage tab and keeps your current page in its tab.

• Upload a JPEG, PNG, or WebP thumbnail, up to 10 MB, and enter a video title.
• Customize the channel name and optionally upload a channel image.
• Apply your draft to a random visible standard video, or select a card yourself.
• Move the preview to another visible video with Randomize position.
• Switch Preview On or Off to compare your draft with the original card.
• Return to Edit Mode to refine your draft. Close the tester to restore the original card.

Your latest draft is saved locally in Firefox and is available when you reopen the tester. No extension account, paid service, analytics, or developer server is involved. Applied previews are displayed inside YouTube's page; they are not published to your channel. YouTube itself continues to operate under its own privacy practices.

This extension previews appearance only. It does not upload videos, publish thumbnails, run A/B experiments, measure click-through rates, or change the original video and channel links.

Supports one preview per tab on the desktop www.youtube.com homepage. Shorts, ads, playlists, search results, watch-page recommendations, Android, and private windows are not supported. YouTube layout changes can affect compatibility. YouTube must show standard home-feed videos; a fresh profile may need viewing history before a feed appears.

Independent project. Not affiliated with or endorsed by YouTube or Google.