ShrinkWatch EU

You're shopping for groceries online and there are two jars of the same thing, in different sizes at different prices. Which one is cheaper? You can't really tell unless you can see the price per kilo. EU shops are required to show a unit price, but online it's often small, missing or inconsistent.

ShrinkWatch EU puts it on the product page. The extension shows the price per kilogram, per litre or per piece, even when the shop doesn't. It works in euros and in eight other currencies, including the Czech koruna, Polish zloty, Swedish krona and Hungarian forint.

The second job gives the extension its name. It remembers the pack sizes of products you've looked at. If a 500 g pack turns into a 450 g pack at the same price, it tells you, in the form "was 500 g, now 450 g, +11.1% per kg". A popup also shows how the unit price of the product you're viewing has changed over time.

The FAQ is upfront about the catch. The extension only knows about products you have looked at before. It has no shared database, so it can't warn you about a change that happened before you installed it. The developer adds that it reads the pack size from the page text, so unusual descriptions such as multipacks, fractions and drained weight can still be missed. When it can't read a reliable size, it shows no number instead of a wrong one, which is the right call.

The site lists 71 grocery and drugstore web shops. They're spread across Germany, Austria, France and Italy, then Spain, Portugal, the Netherlands and Belgium, plus the Nordics, Poland, Czechia and other countries. In the big markets that includes Lidl, Kaufland and Rewe, along with dm and Rossmann. Of the 71, 66 are verified on real product pages. Five aren't yet, because the shop blocks the test browser or needs a login first.

On Firefox it's a one-click install from addons.mozilla.org with automatic updates. On Chrome, Edge and Brave you download a zip file from the project's GitHub releases and load it yourself, which is more fiddly and means no automatic updates from a store.

There's no account, no server and no tracking. The privacy policy in the project's repository says the extension does not collect, transmit, sell or share any data, and runs only on the supported shop domains. According to the developer, the stored history holds the shop, product ID and pack size, along with the price, currency and date seen. The browser deletes it when you uninstall, and Clear stored history in the popup wipes it at any time.

It's free and MIT licensed, published from the GitHub account emirmrkaljevic, and says it isn't affiliated with or sponsored by any retailer. If you do your grocery shopping online anywhere in Europe and like knowing what a kilo really costs, it's worth installing before your next order.