YouTube Thumbnail Preview Enlarger

WHAT IT DOES

YouTube Thumbnail Preview Enlarger is a browser extension that automatically scans the current YouTube page for video thumbnails, thumbnail images, and video preview elements. It detects thumbnail images by examining img elements with src URLs containing "ytimg.com/vi/" and YouTube-specific class patterns. The extension adds a floating enlarge button (🔍) next to each detected thumbnail, allowing you to view thumbnails in high resolution with a single click or hover. Clicking the button opens an overlay with the enlarged thumbnail in high quality (maxresdefault.jpg) with a dark backdrop, video title, and close button. The extension also supports hover-triggered enlargement with a configurable delay. The main panel allows you to adjust zoom level (1x-10x), choose trigger mode (hover or click), preview thumbnails, add notes about video content, and view thumbnail viewing history. The extension maintains a thumbnail database per video with viewing history, view counts, and notes. All data is stored locally in your browser using GM_setValue, ensuring your preferences and history persist across page reloads and browser sessions. This helps YouTube viewers, content researchers, and thumbnail analysts to view thumbnails in larger size for better preview and content assessment, making it easier to evaluate video content before clicking.

WHERE IT RUNS

This extension runs on any YouTube page that displays video thumbnails, thumbnail images, or video preview elements – including YouTube home page, search results, channel pages, playlists, and recommended videos sections. The extension intelligently adapts to different page structures and supports a wide range of common YouTube display patterns. No manual configuration is required per site; the extension automatically detects thumbnail elements using a flexible pattern matching system. This makes it ideal for YouTube viewers, content researchers, and thumbnail analysts who want to preview thumbnails in larger size.

HOW TO USE

Simply install the extension and navigate to any YouTube page displaying video thumbnails. The extension automatically detects thumbnails and places a small enlarge button (🔍) on each thumbnail. Click the button to open a high-resolution enlarged view of the thumbnail in a dark overlay – click anywhere outside or press the close button to dismiss. By default, hovering over a thumbnail for 400ms also triggers the enlargement (configurable). A floating button (🖼️) appears in the bottom-right corner of the page – click this to open the main panel. The panel shows settings for zoom level and trigger mode, allows you to test the enlargement feature, and displays your thumbnail viewing history with view counts and last viewed dates. Use the settings section to adjust zoom level (1-10x), choose between hover and click trigger modes, and enable or disable auto-detection. The "Clear All History" button removes all tracking data when needed.

ONE TECHNICAL SECTION – WHY IT WORKS

The extension employs a multi-layered detection system that identifies YouTube thumbnails with high accuracy. First, it scans the DOM using a comprehensive set of CSS selectors targeting img elements with src URLs containing YouTube video IDs and thumbnail patterns. The video ID extraction uses regex pattern matching to extract the 11-character YouTube video ID from the thumbnail URL or parent link. The high-resolution thumbnail URL is constructed using the YouTube maxresdefault.jpg endpoint. When a user hovers over or clicks a thumbnail, the extension creates a full-screen overlay with the enlarged image, applying the configured zoom level. The overlay includes a dark backdrop, the enlarged image centered in the viewport, video title display, and a close button. The extension also supports hover-triggered enlargement with a debounced delay to prevent accidental triggers. Each thumbnail view is logged with video ID, title, timestamp, and view count. A MutationObserver detects dynamic content updates and re-scans only when new thumbnail elements appear, balancing real-time accuracy with system performance.

THE PANEL – DRAG / PER-SITE POSITION / SNAP / COLLAPSE / RESIZE / ESCAPE

The thumbnail preview panel includes a draggable title bar, allowing you to position it anywhere on screen for convenient access during content browsing. The extension remembers your preferred position per website, so the panel opens in the same location each time you return to that domain. The panel supports snap-to-edge behavior – when dragged near screen edges, it gently snaps into place for a tidy workspace layout. You can collapse the panel down to just its title bar by clicking the collapse button, keeping it accessible without taking up screen space. The settings and history are contained within a scrollable body, ensuring all content remains accessible even on smaller screens. Pressing the Escape key closes the panel instantly, returning you to your browsing workflow.

PLEASE NOTE

This extension requires the free BotGentz extension to be installed and enabled, as it relies on BotGentz's userscript injection and GM_* API shims for cross-browser compatibility. Websites frequently update their HTML structures and class names, which may cause thumbnail detection to break temporarily – we actively maintain the matching patterns and release updates regularly. The extension stores all thumbnail viewing data, preferences, and history exclusively in your local browser storage (GM_setValue); no data is ever transmitted to any external server or third party. The extension does not read, modify, or interfere with any YouTube content, videos, or functionality beyond the thumbnail display – it operates on the page content and stores only metadata (video IDs, titles, view counts, and notes) that you explicitly create. You are responsible for backing up your thumbnail history data if you switch browsers or clear your storage. Use this tool responsibly and in accordance with YouTube's Terms of Service.