Price Change Log

WHAT IT DOES

Price Change Log is a browser extension that automatically scans the current webpage for product prices, currency symbols, and price-related elements. It detects price information by examining class names, IDs, data attributes, and text patterns that contain currency symbols or numeric values. The extension adds a floating button that allows you to capture the current price, product name, and timestamp with a single click. Clicking this button stores the price history locally and opens a panel showing price changes over time. The extension also adds a small "log this price" button next to each detected price element on the page, making it easy to record prices without opening the main panel. Price history is maintained per product URL, with each entry storing the date, price, and an optional note. The panel displays price trends, calculates percentage changes, and visually highlights price drops in green and price increases in red. All price history is stored locally in your browser using GM_setValue, ensuring your data persists across page reloads and browser sessions.

WHERE IT RUNS

This extension runs on any webpage that displays product prices – including e-commerce websites, online marketplaces, retail stores, auction sites, price comparison platforms, and any other page showing product or service prices. It works wherever there is a visible price element on the page. The extension intelligently adapts to different page structures and supports a wide range of common pricing display patterns. No manual configuration is required per site; the extension automatically detects price elements using a flexible pattern matching system.

HOW TO USE

Simply install the extension and navigate to any product page or website showing prices. The extension automatically detects price elements and places a small "log this price" button next to each one. Click any of these buttons to instantly log the current price for that product. A floating button appears in the bottom-right corner of the page – click this to open the main panel. The panel shows the current product name, the latest price, and a complete history of all logged prices. Each entry displays the date, time, price, and any notes you've added. The panel calculates and displays the total price change and percentage change since your first log, with visual indicators showing whether prices have increased or decreased. Use the "Log Current Price" button to manually log the price, or "Log with Note" to add a custom note to the entry. The extension can also auto-log prices on page load if you enable this feature in settings.

ONE TECHNICAL SECTION – WHY IT WORKS

The extension employs a multi-layered detection system that identifies price information with high accuracy. First, it scans the DOM using a comprehensive set of CSS selectors targeting common price-related class patterns, IDs, and data attributes. Second, it uses a TreeWalker to examine text nodes for currency symbols and price patterns, capturing prices that may not be wrapped in typical price elements. The price extraction algorithm uses a weighted scoring system that considers multiple factors: proximity to product names, currency symbol presence, and historical price patterns. The extension generates a unique fingerprint for each product based on the full URL with tracking parameters removed, ensuring that price history stays correctly associated even when pages use different query strings. All storage operations are wrapped in try-catch blocks with graceful fallbacks, ensuring the extension never breaks page functionality. The extension uses a MutationObserver to detect dynamic content updates and re-scans only when new price elements appear, balancing performance with accuracy.

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

The main price history panel includes a draggable title bar, allowing you to position it anywhere on screen for convenient access. 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 price history list and metrics 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 experience.

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 price detection to break temporarily – we actively maintain the matching patterns and release updates regularly. The extension stores all price history, timestamps, and notes exclusively in your local browser storage (GM_setValue); no data is ever transmitted to any external server or third party. You are responsible for backing up your price tracking data if you switch browsers or clear your storage. The extension does not read, modify, or interfere with any payment processing or checkout functionality – it operates solely on the static page content and stores only metadata (prices, timestamps, and notes) that you explicitly create.