There is an app called Yuka, that is like that. Scan the barcode and it tells you which red flag ingredients are in it.
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Exactly!
I am developing one with a slightly different goal.
The app is searching the online catalog of supported shops, to find the healthiest alternative. So you know what to buy in the shop you go to.
The goal is to find a healthiest option for a category, e.g. cookie, in a specific supermarket.
Shortcomming: your shop has to have an online catalog to be supported.
That's awesome!