Every verdict on this site is an automated judgment built from two parts: label data from Open Food Facts, and a rule engine we wrote and keep tuning. You should know how both work, including where they fail.
The data
Open Food Facts is a nonprofit, crowdsourced database of packaged food, published under an open licence (ODbL). Volunteers photograph labels and transcribe ingredients. That model gives it a scale no company database matches, 28,601 of its products are in our checker right now, and it also means the data inherits human error: outdated photos, typos, missing nutrition tables. When the data is missing or ambiguous, our answer says so instead of papering over it.
The rules
Each diet is a fixed rule set, not an opinion. Vegan and gluten-free checks scan ingredients and allergen data against keyword lists that cover seven languages, because a French label declares milk as "lait" and an English-only scan misses it. We learned that one from a reader. Keto is pure arithmetic on the macro table: at most 10g carbs and 5g sugars per 100g, and no macro data means no confirmation. Halal distinguishes clear violations from Mushbooh, the doubtful additives whose origin a label cannot prove, and tells you which is which.
The bugs, in the open
Two recent ones, because a checker you cannot audit is just vibes. First, the French label problem above: before the fix, thousands of non-English products could show a wrong green. An audit after the fix moved 5,343 products from a wrong yes to a firm no. Second, an early import script had written all-zero nutrition values into 1,311 products, which briefly let a KitKat pass a keto check. We re-pulled the real numbers for every affected product and added a guard that treats suspicious zeros as missing data.
What this means for you
Treat our verdicts as a fast, honest first pass, not a certificate. When we say yes, the label supports it. When we say no, we name the ingredient that decided it. When we say check the label, that is the truthful answer, and the page tells you exactly what is unverified. And when you catch us wrong, write to hello@eatcheck.org. The best fixes in this engine started as reader emails.