How Munchable built an allergen system that can only warn, never falsely clear

Munchable, an app helping people with IBS or reflux assess supermarket products, expanded in September 2024 to also flag declared allergens. Unlike its dietary condition logic, the allergen layer is designed to only add warnings and never mark a product as allergen-free, since absence of data is treated as silence rather than safety. This rule is enforced at three levels — in code logic, in result structure, and in a TypeScript type that contains no value for 'absent'. The system covers all 14 EU and UK regulated allergens, a superset of the US 'big nine', so warnings are not lost when users travel across regions. Careful distinctions are also made to avoid false positives, such as not treating an inferred generic 'nut' tag as evidence of peanuts unless that word appeared on the physical label.