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Curiosity Diaries

YouTube Thumbnail Tester

Preview your thumbnail in the feed.

  • 100% free
  • No sign-up
  • Runs in your browser

Will it stand out at 120 pixels wide?

A thumbnail that looks great full-screen can turn to mush in the sidebar or on a phone. This tester drops your image and title into realistic YouTube layouts so you can judge it at the size viewers actually see.

It also checks the 1280×720 resolution, 16:9 aspect ratio and YouTube's 2 MB upload limit.

  1. 1

    Choose your thumbnail

    It never leaves your device.

  2. 2

    Type the title

    And your channel name.

  3. 3

    Compare views

    Home, up next and mobile — light and dark.

Frequently asked questions

What size should a YouTube thumbnail be?

1280×720 pixels (16:9), at least 640 pixels wide, as JPG, PNG or GIF under 2 MB.

Why test in dark mode?

Most viewers use YouTube in dark mode on mobile; dark-edged thumbnails can disappear against the background.

Is my data uploaded anywhere?

No. Everything runs in your browser with JavaScript — nothing you type or open is sent to our servers.

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