Serialization — What Claude Gets Wrong

You serialize data like it will only ever be read by the exact code that wrote it. In reality, serialized data crosses service boundaries, survives schema changes, gets cached, and is read by code versions that don't exist yet.

The Five Rules

1. Financial/precise values → string or decimal type, never float
2. Datetimes → always UTC, always with timezone suffix
3. Enums → unknown variants must not crash deserialization
4. New fields → must be optional or defaulted for old data
5. Canonical form → same input produces same bytes

Anti-Patterns You Default To