Mercari Offer History Overlay

WHAT IT DOES

Mercari Offer History Overlay scans Mercari listing pages and displays a comprehensive panel showing the complete offer history for the current item. It extracts offer data including amounts, timestamps, and statuses (pending, accepted, declined, expired). A summary panel shows total offers, highest offer, lowest offer, and average offer amount. A visual bar chart displays offer amounts over time, and the best offer is highlighted with a star icon. An offer timeline lists each offer with its amount, status, and buyer name where available. This gives you valuable insight into how much other buyers are willing to pay, helping you make smarter purchasing decisions and understand the true market value of an item.

WHERE IT RUNS

This script runs on Mercari listing pages (*.mercari.com/*). It operates entirely within your browser tab, reading the page's DOM to locate offer history sections, transaction data, and pricing information. The script cannot access other tabs, your browsing history, bookmarks, downloads, or any data outside the current page. All settings—including offer timeline visibility, price chart visibility, best offer highlighting, status color display, auto-detect preference, and refresh interval—are stored locally using GM_setValue and never transmitted anywhere.

HOW TO USE

After installing with the BotGentz extension, the script automatically detects Mercari listing pages and displays the offer history overlay (if auto-detect is enabled). The panel shows a summary of offer statistics, a price chart, and a detailed offer timeline. Click "Load Offer History" to manually refresh the data. Customize the display: toggle the offer timeline on or off, show or hide the price chart, highlight the best offer with a star, and show status colors for each offer. Set the refresh interval (5-300 seconds) to keep the data up to date. Click "Copy Offer Summary" to copy a formatted summary to your clipboard for analysis or sharing.

THE REAL MECHANISM

The script detects Mercari offer data by scanning the page for offer history containers using selectors like .offer-history, .offer-list, .transaction-history, and .offers-section. It extracts offer rows using .offer-row, .offer-item, or .transaction-row selectors, parsing the text content to extract offer amounts (looking for ¥ symbols or Japanese currency markers), statuses (accepted, declined, expired, pending), timestamps (in various date formats), and buyer names. If no structured offer container is found, the script falls back to scanning the entire page for rows containing price markers and offer-related keywords. The offer statistics are calculated from the extracted data, and the price chart is rendered as a bar chart where bar height represents the offer amount relative to the highest offer. The best offer is identified as the highest amount among all offers. All DOM manipulation uses safe methods with no innerHTML from untrusted content.

THE PANEL

The Offer History panel is a BGPanel component that you can drag anywhere on your screen by its header. It snaps to the nearest edge when released, keeping your workspace organized. The panel collapses to a small bubble showing only the emoji icon when minimised—click to expand it again. You can resize the panel horizontally to see more of the offer timeline. Press the Escape key to collapse the panel instantly. Your panel position and size are saved per-site.

PLEASE NOTE

This script requires the free BotGentz browser extension to function. Mercari frequently updates its UI, which may change class names, data-testid attributes, and DOM structure—the script may require updates to maintain compatibility. The offer history extraction relies on the presence of offer data on the page; if the listing has no offer history or the offer section is not loaded, the script may not detect any data. The price chart is a visual approximation and may not be perfectly accurate for all listings. The script never reads or writes password fields, hidden inputs, or file inputs. It stores only your offer timeline visibility, price chart visibility, best offer highlighting, status color display, auto-detect preference, and refresh interval locally. No offer data, listing information, or personal information is ever collected, transmitted, or shared.