Error Handling

Error Handling Patterns

Consistent, robust error handling patterns for production applications.

When to Activate

• Designing error types or exception hierarchies for a new module or service
• Adding retry logic or circuit breakers for unreliable external dependencies
• Reviewing API endpoints for missing error handling
• Implementing user-facing error messages and feedback
• Debugging cascading failures or silent error swallowing

Core Principles

1. Fail fast and loudly — surface errors at the boundary where they occur; don't bury them
2. Typed errors over string messages — errors are first-class values with structure
3. User messages ≠ developer messages — show friendly text to users, log full context server-side
4. Never swallow errors silently — every catch block must either handle, re-throw, or log
5. Errors are part of your API contract — document every error code a client may receive

TypeScript / JavaScript

Typed Error Classes