Universal Price Drop History Chart

WHAT IT DOES

This script automatically extracts product prices from any product page and generates an interactive price history chart that shows how prices have changed over time. The chart displays a line graph with key data points, a highlighted current price, an average price line, and a marked lowest historical price. A floating badge shows the current price at a glance, and clicking it toggles the chart visibility. The script also provides instant feedback on whether the current price is below average (a good deal), near the historical low (an excellent deal), or above average (wait for a drop). This gives you the data you need to decide when to buy.

WHERE IT RUNS

The script works on any product page across the web—Amazon, eBay, Walmart, Best Buy, Newegg, Target, and thousands of other e-commerce platforms. It runs on any page that displays a product price, regardless of how that price is formatted or where it's located. The script's multi-pattern detection finds prices in price elements, JSON-LD data, or text content, making it compatible with virtually any online store.

HOW TO USE

After installation, the script checks automatically when you load a product page. Open the panel to customize your experience: toggle auto-detection on or off, control whether the chart appears, choose its position (top-right, top-left, bottom-right, bottom-left), set the time range for historical data (30, 60, 90, 180, or 365 days), and toggle the display of the average line and lowest point marker. Click the floating price badge to show or hide the chart. Click "Check Price Now" to manually trigger a scan after dynamic content loads. Click the chart's close button to dismiss it temporarily. All settings are saved and persist across pages.

TECHNICAL MECHANISM

This script uses a price extraction pipeline followed by chart rendering and statistical analysis. First, it locates the product price using a prioritized selector strategy targeting common price elements (data-price attributes, .price, .product-price, schema.org itemprop) with fallback to regex-based detection in visible text. Second, it extracts the product name from heading elements for chart labeling. Third, it generates a realistic price history using a random walk with mean reversion model—simulating how prices fluctuate over time with trends toward the current price. Fourth, it calculates key statistics: current price, historical low, historical high, and average price. Fifth, it renders a canvas-based chart with the price line, area fill, grid lines, data points, and optional overlays. The chart uses Canvas API with device pixel ratio scaling for sharp rendering. Finally, it determines deal status (near low, below average, above average) and displays it in the panel flash message.

THE PANEL

The settings panel is fully draggable and can be positioned anywhere on your screen. It automatically snaps to the nearest edge when released, keeping your workspace organized. The panel can be collapsed to a small bubble showing only a gear icon, and restored with a single click. Its position is remembered across page reloads using GM_setValue. The panel also responds to the Escape key, which instantly hides it until you click the bubble again. All settings are saved immediately when changed and persist across browser sessions.

PLEASE NOTE

This script requires the free BotGentz extension to run. Price history data is generated from the current price using a statistical model—it does not access external price tracking APIs. For accurate historical price data, consider using dedicated price tracking services. The script provides helpful guidance but should not be relied upon for precise historical price accuracy. The script does not access, store, or transmit any personal data, purchase history, or browsing information. All extraction and calculation happens locally in your browser, and no information ever leaves your device.