BuyMax – Max Buy Price & Risk Checker

Calculates a safe max buy price and checks counterfeit/resale risk on Amazon product pages, before you buy.

**"How much can I pay for this, and is it safe to resell?"** BuyMax answers both questions on the Amazon product page itself, in under a second. **Safe max buy price (free).** Set your target ROI and BuyMax works backward from the current price — referral fee, category closing fee, FBA or self-ship cost — to a safety-margined maximum buy price. Every number comes with a confidence badge (High/Medium/Low) so you know when the estimate is solid and when it's a rough guess. A final-check checklist and a direct link to Amazon's official Revenue Calculator keep you from over-trusting a single number. **Risk sensor (Pro).** Before you buy, BuyMax checks the product title against a maintained local database of brands known for frequent counterfeit/IP investigations, manufacturers that restrict resale in their terms, regulated categories that need approval, and "new condition" pitfalls — each with a reason, a public source link, and an update date. No hit is ever shown as "safe" — only "no known match," because absence of evidence isn't evidence of safety. **Everything else:** a one-click watchlist with CSV export (Pro), cross-marketplace search launchers (Mercari, Rakuten, Yahoo! Auctions, Suruga-ya, 2nd Street — you click, we never auto-crawl), and a one-click "copy for AI" button that hands your research to ChatGPT/Gemini as structured Markdown+JSON. **Free 14-day Pro trial**, no credit card required to install. **Privacy first.** BuyMax reads only the Amazon product page you have open, only inside your browser, and only after you explicitly consent on first run. Your watchlist and notes never leave your device. Full privacy policy linked below. **v1 coverage:** amazon.co.jp is fully supported (calculator + risk sensor) across 5 major categories (Books, CD/DVD/Music, Video Games, Toys & Hobby, Electronics & Camera accessories). amazon.com support is an early calculator-only beta — the risk sensor is JP-first, US coming soon. ## Category Productivity / Shopping ## Permission justifications (for the CWS reviewer) - `storage`: stores your settings, watchlist, and trial/license state locally in `chrome.storage.local`. Nothing here is synced to any BuyMax server — we don't have one. - `sidePanel`: hosts the full calculator UI (Side Panel), separate from the compact on-page card. - `alarms`: wakes the background service worker roughly once an hour to refresh your Pro subscription status from ExtensionPay (so a completed payment is reflected even if you don't reopen the Side Panel/Options page right away) and to check for the monthly fee-table/risk-database update. No new data is read by this permission — it is a timer only. - `host_permissions` (`https://www.amazon.co.jp/*`, `https://www.amazon.com/*`): the content script reads visible product data (title, price, category, ASIN) only on these two domains, only to run the calculator and risk check locally. No other site is ever read. No background/automatic crawling of any kind. - No remote code: all calculation logic ships inside the extension. The only network calls are (1) a monthly fetch of a static, schema-validated JSON file (fee tables / risk database) from our GitHub Pages site, and (2) ExtensionPay/Stripe for Pro subscription checkout and license verification (also triggered periodically by the `alarms` timer, not just when you click Subscribe). ## Screenshots shot-list (for the owner to capture before submission) 1. Amazon product page with the floating compact card showing a safe max buy price + confidence badge + risk indicator. 2. Side Panel — full calculator view with the fee breakdown table visible. 3. Side Panel — risk detail list showing a real risk-DB hit with reason/source/updated date. 4. Onboarding consent screen (first run). 5. Options page — language/ROI/safety-margin/marketplace settings. 6. Watchlist with a couple of saved items and the CSV export button. 7. (Optional) Dark-mode screenshot of the compact card, to show theme awareness. ## Support / Privacy links - Support: Chrome Web Store support tab, or the GitHub repository issue tracker (see README.md for the URL the owner should publish). - Privacy Policy: hosted copy of docs/PRIVACY.md — see README.md "Owner setup steps" for the publishing step.