Thumbnail A/B Tester한국어

About Thumbnail A/B Tester

What is This Tool?

Thumbnail A/B Tester is a free, browser-based tool for YouTube and blog creators to compare thumbnail candidates and score them on 5 CTR (click-through rate) optimization criteria. Upload 2–4 thumbnails, check off each quality criterion, and instantly see which thumbnail is likely to perform best.

Unlike many online thumbnail tools, this tool processes everything entirely in your browser — no images are uploaded to any server. Your thumbnails remain private.

Key Features

  • Side-by-side comparison: View 2–4 thumbnails simultaneously for direct comparison.
  • Actual size preview: Preview thumbnails at 4 real YouTube display sizes: Mobile Feed (320×180), Search Result (246×138), Recommended (168×94), and Desktop (480×270).
  • CTR checklist scoring: Score thumbnails on 5 evidence-based criteria, each worth 20 points (100 total).
  • Aspect ratio check: Automatically detects if your thumbnail matches YouTube's recommended 16:9 ratio.
  • Item-by-item comparison: See exactly where your thumbnails differ in score across each criterion.
  • 100% client-side: No server upload, no login, no data collection. Scores are saved locally in your browser.
  • Korean/English bilingual: Full support for both Korean and English interfaces.

How Scores Are Calculated

The CTR score is based on a 5-item checklist, each worth 20 points:

  1. Text Readability (20pts): Is the text clearly readable at thumbnail size?
  2. Color Contrast (20pts): Is there sufficient contrast between background and text/elements?
  3. Face/Emotion (20pts): Is there a clear face or strong emotional expression?
  4. Whitespace (20pts): Is whitespace well-utilized for visual comfort?
  5. Brand Consistency (20pts): Is the thumbnail consistent with your channel's brand/style?

These criteria are based on widely published research on YouTube CTR optimization, including studies by channels with 1M+ subscribers and YouTube's own creator documentation.

Privacy Policy

This tool does not collect, store, or transmit any image data. Thumbnail images are processed entirely within your browser using browser-native APIs (FileReader, URL.createObjectURL). Checklist scores are stored only in your browser's localStorage and are not accessible to any server. We use Google Analytics 4 (with consent mode) for anonymous usage statistics.

Disclaimer

CTR scores generated by this tool are reference values based on general best practices. Actual click-through rates depend on your content topic, audience, publication timing, and YouTube's algorithm — factors outside the scope of thumbnail design. Use scores as a comparative tool, not an absolute predictor.

About bal.pe.kr

This tool is part of the bal.pe.kr micro-SaaS collection — a suite of free, browser-based productivity and utility tools. All tools are free to use, with no account required.

Contact: comsamo84@gmail.com