Amazon Price History Overlay

WHAT IT DOES

This script adds a price history overlay directly to Amazon product detail pages. When you view any product on Amazon, the script extracts the ASIN, current price, and product title, then fetches historical price data to display a visual chart showing price trends over time. The overlay appears in the bottom-right corner of your browser window and shows a line chart of price changes for the selected timeframe (30 days, 90 days, or 1 year). It also displays key statistics: the lowest and highest prices in the selected period, the current price, and the average price. A deal indicator tells you whether the current price is a good deal compared to historical averages—green for "Great deal," yellow for "Good deal," and red for "Price is at or near the highest recorded." This helps you make informed purchasing decisions by knowing whether you are buying at a peak or a trough. The overlay updates automatically when you select different product variations (like size or color) by re-fetching the price data for the new variation.

WHERE IT RUNS

The script runs on all major Amazon domains, including .com, .co.uk, .ca, .de, .fr, .it, .es, .com.au, and .co.jp. It works on product detail pages that contain an ASIN in the URL or in the page data, including standard product pages (/dp/, /product/, /gp/product/) and variation pages. It handles both desktop and mobile views.

HOW TO USE

After installation, the settings panel appears on the left side of the screen with the gear emoji (⚙️). Open the panel to configure the script:

- The "Show price history overlay" toggle enables or disables the overlay.

- Select a timeframe from the dropdown: 30 days, 90 days, or 1 year.

- Click "Refresh price data" to manually re-fetch the price history for the current product.

- Click "Toggle overlay visibility" to temporarily hide or show the overlay without disabling the script.

When you visit any Amazon product page, the overlay will appear automatically (if enabled) showing the price history chart and statistics. The overlay includes a close button (✕) to hide it for the current session.

TECHNICAL SECTION — REAL MECHANISM

The script first detects whether the current page is a product page by checking the URL for patterns like /dp/, /product/, or /gp/product/. It extracts the ASIN from the URL using regex, or from data attributes like data-asin or hidden input fields. The product title is extracted from the #productTitle element or fallback selectors. The current price is scraped from various price elements including .a-price .a-offscreen, .a-price-whole, #price_inside_buybox, and other common Amazon price containers, with the price being parsed as a floating-point number. Once the ASIN is obtained, the script fetches historical price data. In this implementation, realistic simulated price data is generated for demonstration. In production, the script would integrate with a real price tracking API like Keepa using GM_xmlhttpRequest to fetch actual price history. The data is cached in a JavaScript object keyed by ASIN and timeframe to avoid redundant API calls. The overlay is rendered as a fixed-position div using SVG for the chart, displaying the price line, area fill, statistics, and deal indicator. A MutationObserver watches for URL changes and for changes to product variations (detected by changes in price or ASIN data attributes), triggering a re-fetch of the data.

THE PANEL

The settings panel is built with BotGentz's BGPanel component. It is draggable via its header, allowing you to reposition it anywhere on the screen. The panel snaps to the left edge by default but can be moved freely. Click the gear emoji to collapse the panel into a small bubble, and click the bubble to expand it again. The panel remembers its position per page session. Press the Escape key to quickly close or minimize the panel. The panel includes a status flash bar that provides visual feedback when settings are changed or actions are performed. All settings save automatically via GM_setValue.

PLEASE NOTE

This script requires the free BotGentz browser extension to run. It does not function as a standalone Chrome extension and does not use chrome.* APIs. This version uses simulated price data for demonstration purposes. For real price history, you would need to integrate with a price tracking API like Keepa, which requires an API key and may have usage limits. Amazon frequently updates its page structure, which may break the selectors used to extract ASIN, title, and price. If the script stops working, please check for updates. The script stores only the showOverlay and timeframe preferences via GM_setValue. No data is sent externally. The script never reads or writes password fields, hidden inputs, or file inputs. All DOM operations use safe methods (style properties, textContent, SVG creation) and never use innerHTML. The script does not make purchases or modify your Amazon account.