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Thumbnail & Cover Legibility Checker

See your thumbnail the way viewers do — tiny, in real feeds — and get concrete fixes for text size, contrast, face size and clutter. Everything runs on your device.

Free · No sign-up

How to use Thumbnail Legibility Checker

  1. 1. Drop your thumbnail or cover (JPG, PNG or WebP). It is analysed in your browser — nothing is uploaded.
  2. 2. Look at the previews: each feed slot is drawn at its real width with the app's crop, length badge, buttons and safe zones. Switch light/dark mode or try the squint test.
  3. 3. Read the score and checks: smallest text size on screen, word count, text contrast, face size, clutter and anything hidden under the app's UI — with a list of concrete fixes.
  4. 4. Made a new version? Click Compare with another version to see both side by side with their scores.

Frequently asked questions

How does the checker know if my text is readable?

It reads the text on your image with on-device OCR, measures each line's height and works out how many pixels tall it will be in each feed slot, such as the 168-pixel YouTube “Up next” thumbnail or the 124-pixel Instagram grid. Under about 9 pixels most people can't read it at a glance.

Is my thumbnail uploaded?

No. Text and face detection run in your browser with Tesseract.js and MediaPipe, which download their engines once (about 5 MB). Your image never leaves your device.

Which platforms and sizes are previewed?

YouTube home, mobile feed and “Up next”, the YouTube Shorts shelf, the Instagram and TikTok profile grids, and full-screen TikTok, Reels and Shorts, each with that app's crop and on-screen buttons. Layouts change often, so treat overlays as a guide.

What counts as good contrast for thumbnail text?

The checker compares the text colour with what's behind it using the WCAG contrast formula. 4.5:1 or more reads well even when small; below 3:1 text tends to vanish. An outline, drop shadow or solid band behind the words fixes most cases.

Why does the face size matter?

Expressions are one of the main things people notice in a small thumbnail. When a face fills less than about a third of the height, it shrinks to a few pixels in side-bar and grid views. You can change this threshold to suit your style.

Can I compare two thumbnail versions?

Yes. After checking one image, click Compare with another version and add the second. Both are scored with the same rules and shown side by side in every feed, so you can pick the one that reads better.