Visual Design

Thumbnail Readability Lab

Upload a thumbnail to inspect dimensions, aspect ratio and file size, then preview it at phone scale. Contrast diagnostics run on a local canvas. Images stay in this page unless you download the audit summary.

How to use it

  1. Choose a PNG, JPG or WebP file under 8 MB.
  2. Inspect the full and small-screen previews.
  3. Optionally add up to three images to a side-by-side comparison.

This page never sends the image to a server in Part 1. If a future version does, you will see a warning first.

Audit

Upload a thumbnail to inspect it locally.

Compare up to three

No comparison images yet.

Privacy

Files are read with FileReader in your browser. ToolUpa does not permanently retain uploads. Refreshing the page clears them.

Related tools

    FAQ

    Do you detect faces or OCR text?

    No. Part 1 reports size, ratio, file weight and a simple light/dark contrast hint.

    Why 8 MB?

    Large files can freeze a tab when drawn to canvas. Keep source files reasonable.

    Is the small preview the same as YouTube mobile?

    It is a 160px-wide stand-in, not an official YouTube UI clone.