The batchcodecheck.com site answers one question: when was this cream made. Batch Code Checker: Cosmetics brings that answer to the shelf, where people actually stand holding a package. You type the code or photograph it, and the app shows the production date, the product's age and the rule the date came from.

The app does not decide dates on its own. Every check goes to the same engine the site runs, so a rule fixed on the site reaches every install that minute, with no store release. Offline, a built-in copy of the engine answers and the result card says so. Each rule in the engine is a small decode function rather than data, which is why it lives on the server and not in a downloadable file.

When a brand's scheme is not confirmed, the app says that instead of inventing a date. A wrong date is worse than none, so confirmed and preliminary answers are marked differently. Typing a code is free and unlimited; photo reading has a small daily allowance, and a one-time Pro purchase removes the banner and lifts the limit. No account, history stays on the phone.