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API Contracts That Age Well

Notes on predictable resource models, validation errors, pagination, and compatibility as a backend API grows.

APIs age well when clients can predict their behavior. Naming, status codes, validation, and pagination all contribute to that predictability.

Resource shape

Use stable resource names and response fields. Avoid exposing database details that may change later.

Validation errors

Validation responses should tell clients what failed and where. A consistent error model saves time across every consumer.

Compatibility

Breaking changes are expensive. Add fields carefully, keep old behavior working when possible, and version only when the contract truly changes.