Stored only on this device (never uploaded, never in the app's source code). Get a free key at fdc.nal.usda.gov/api-key-signup if you outgrow the shared demo limit (30 searches/hour).
Signing in lets every food and workout log also write to your private Supabase database, so a Nippard or Sevro session can read it when you ask for analysis. Nothing changes about what's stored on this phone. This only adds a copy going out, and only for entries logged while signed in and online.