Event Schema

An event schema is an event's defined structure: its name, the properties it carries, each property's data type and its allowed values — a contract that fixes the shape of the data.

An event schema is what turns an event from an arbitrary message into reliable data: when the schema is clear, everyone knows purchase definitely has an amount property of numeric type and a currency from an allowed list. Its value is predictability; reports are built on the assumption that today's data has the same shape as yesterday's. The schema's biggest enemy is its gradual drift: if one app version sends amount as a string instead of a number, or a new value appears outside the allowed set, the schema quietly breaks and reports become wrong without raising an error. So a schema is not just an initial definition but a continuous commitment to validation. A good schema is stable, documented and validated.