TypeScript API Contracts That Survive Product Growth
Design TypeScript contracts with validation, versioning, narrow DTOs, and explicit error states so APIs remain stable as teams scale.
Treat external data as unknown
Network responses, user input, webhooks, and files should be validated at the boundary. Runtime schemas make failures visible and actionable.
Keep DTOs narrow
Expose only the fields each route needs. Narrow data transfer objects reduce coupling and make later migrations less painful.
Model errors explicitly
Return clear error codes, messages safe for users, and diagnostic details safe for logs. Avoid making every caller parse exception text.
Version when behavior changes
Additive fields are easy. Changed semantics require versioning, migration notes, and compatibility tests.
Frequently asked questions
Why validate data if TypeScript already has types?
TypeScript checks source code, but runtime validation checks external data that can arrive malformed or incomplete.
Author
Elena Patel
Elena focuses on programming tutorials, software architecture, and productivity systems.