What Is API Versioning? Backward-Compatible API Design

Does adding new fields break existing clients? Unsure when to remove old endpoints? API versioning lets you evolve your API without breaking consumers.

Versioning Strategies

1. URI Versioning (Recommended)

GET /api/v1/users/42
GET /api/v2/users/42

2. Header Versioning

Accept: application/vnd.myapp.v2+json

3. Query Parameter

GET /api/users/42?version=2

Breaking vs Non-Breaking Changes

Breaking: Adding required fields, removing fields, changing response structure Non-Breaking: Adding optional fields, new endpoints, new optional parameters

Deprecation Strategy

1. Announce deprecation | 2. Add Sunset header | 3. Give 6-12 month transition | 4. Monitor usage | 5. Remove when usage near zero

Best Practices

1. Avoid versioning when possible — Prefer backward-compatible changes
2. URI versioning for clarity
3. Maximum 2 active versions
4. Deprecation policy — Minimum 6 months
5. Keep API docs current — Swagger/OpenAPI

Conclusion

API versioning lets you evolve without breaking clients. URI versioning is the most common approach, but the best strategy minimizes the need for versioning through backward-compatible design.

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