error-handlinglisted
Install: claude install-skill TeiNam/my_harness_for_claude_code
# 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
```typescript
// Define an error hierarchy for your domain
export class AppError extends Error {
constructor(
message: string,
public readonly code: string,
public readonly statusCode: number = 500,
public readonly details?: unknown,
) {
super(message)
this.name = this.constructor.name
// Maintain correct prototype chain in transpiled ES5 JavaScript.
// Required for `instanceof` checks (e.g., `error instanceof NotFoundError`)
// to work correctly when extending the