1. API errors are contracts
A successful response is not the only part of an API contract. Clients also need to know how validation, authentication, conflict and server errors are represented. Without that predictability, the user interface becomes fragile.
Good validation responses explain what failed, where it failed and how the client can present the problem without parsing random text.
- Use consistent status codes for validation, authentication and conflict.
- Return field-level errors when a field caused the failure.
- Keep user-facing messages separate from internal technical details.
- Include a stable error code when the frontend needs conditional behavior.
- Avoid changing error formats without version or migration notes.
2. Problem details make errors easier to automate
A structured error format helps web and mobile clients handle failures consistently. Problem details style responses can include type, title, status, detail, instance, field errors and correlation identifiers.
The goal is not to expose every internal detail. The goal is to give enough context for the client, logs and support team to connect the same failure.
- Include request or correlation ID in important failures.
- Keep validation field names aligned with API DTOs.
- Use a predictable array for field errors.
- Avoid leaking stack traces or database names.
- Document examples for common validation cases.
3. Frontend and mobile apps depend on error discipline
A React or React Native app should not guess whether an API failure is recoverable. It needs to know if the user can fix a field, retry later, refresh authentication or contact support.
When API errors are designed deliberately, forms, offline queues and dashboards become easier to maintain.
- Map field errors directly to form controls.
- Show global errors when the problem is not tied to one field.
- Treat retryable errors differently from validation errors.
- Test API error responses with frontend and mobile flows.
- Keep logs searchable by error code and request ID.
How to use this article
Treat this page as a decision aid. Use it with the related hub, checklist or service route when the topic affects production, customer experience, deployment, security or business continuity.