2. APIs & Backend Design
API Contracts, Validation & Versioning
Design APIs that remain predictable as clients and servers evolve independently.
Lesson overview
Validate inputs at the boundary and design additive API changes wherever possible. Compatibility matters because mobile clients, background jobs and external integrations may upgrade at different times.
Learning path
Theory → Example → Code → Practice → Quiz → Challenge → Completion
Step 1
Theory
Validate inputs at the boundary and design additive API changes wherever possible. Compatibility matters because mobile clients, background jobs and external integrations may upgrade at different times.
Step 2
Example
Adding an optional timezone field is usually compatible; silently renaming an existing field is not. A migration period can support both representations.
Step 3
Code
typescript
const input = schema.parse(requestBody);
const result = await service.update(input);
Step 4
Practice
Review your current application and apply API Contracts, Validation & Versioning. Document the current behavior, one production risk, the change you would make, and how you would verify it.
Step 5
Quiz
1. What is the central production concern in "API Contracts, Validation & Versioning"?
Step 6
Challenge
Design a production-ready implementation for API Contracts, Validation & Versioning. Include failure handling, security considerations, observability, testing and a rollback or recovery path where applicable.
Complete every stage
Work through every step in order, then the lesson will be marked complete.
Each chapter and subtopic has its own public URL under /full-stack-to-production.