About Thumb Checkup

Thumb Checkup is made by Thumb Checkup for creators who want to preview a video thumbnail and title before publishing.

The tool shows one uploaded thumbnail across YouTube-style home, search, sidebar, recommended, mobile, tablet, and TV layouts. It also checks local visual signals such as brightness, contrast, color energy, dominant colors, title clipping, and small-detail readability.

Thumb Checkup runs in the visitor's browser. It does not require login, does not add a watermark, and does not upload the thumbnail to a server.