error-handling

What this skill does

When applied, it prepends a system prompt before your request is sent — no extra calls and no change to how you are billed beyond the added tokens.

---
name: error-handling
description: Patterns for robust error handling across TypeScript, Python, and Go. Covers typed errors, error boundaries, retries, circuit breakers, and user-facing error messages.
origin: ECC
---

# 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 built-in Error class.
    Object.setPrototypeOf(this, new.target.prototype)
  }
}

export class NotFoundError extends AppError {
  constructor(resource: string, id: string) {
    super(`${resource} not found: ${id}`, 'NOT_FOUND', 404)
  }
}

export class ValidationError exten

Use this skill

{
  "model": "gpt-4o-mini",
  "skill": "imp-942c602e-4dd9-4303-865f-70ed5ef5dcf2",
  "messages": [{ "role": "user", "content": "…" }]
}

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