truediscount is a free, MIT-licensed browser extension and userscript that checks EU discount claims on the product page. It reads the shop's own 30-day lowest-price label when one is there, compares it with the claimed old price, and shows a badge: a real discount, an inflated one, or that the item was cheaper recently. It also flags a crossed-out price that is only the manufacturer's RRP, keeps a small local price graph, and has a watchlist, price alerts, and JSON or CSV export. It works on shops including Amazon EU stores, Zalando, MediaMarkt, Saturn, Otto, Allegro, bol.com and Coolblue, and any other shop can be turned on from the popup. Everything stays in the browser, with no account and no analytics.
I got tired of Black Friday tags that looked like huge cuts, then checking the shop's own 30-day lowest-price line and seeing the item had been cheaper the week before. EU law already asks shops to use that 30-day low as the reference, but it is easy to miss on the page, and some crossed-out prices are only an RRP. I built truediscount so the comparison sits on the product page. History stays on the device. I do not need an account, and the extension does not call out to my servers.