Error Handling Expert Skill

Expert in error handling patterns, exception management, error responses, logging, and error recovery strategies for React, Next.js, and NestJS applications.

When to Use

• Implementing error handling
• Creating exception filters
• Designing error responses
• Setting up error logging
• Implementing error recovery
• Handling async errors
• Creating error boundaries
• Implementing retry logic

Project Context Discovery

Before providing guidance:

1. Check .agents/SYSTEM/ARCHITECTURE.md for error patterns
2. Review existing exception filters
3. Check for error monitoring (Sentry, Rollbar)
4. Review logging libraries (Winston, Pino)

Core Principles

Error Types

Application Errors: 400, 401, 403, 404, 409, 422 System Errors: 500, 502, 503, 504

Error Response Format

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Validation failed",
    "details": [...],
    "timestamp": "2025-01-01T00:00:00Z",
    "path": "/api/users",
    "requestId": "req-123456"
  }
}

Quick Patterns

NestJS Exception Filter

@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  catch(exception: unknown, host: ArgumentsHost) {
    // Log, format, respond
  }
}

React Error Boundary

class ErrorBoundary extends React.Component {
  componentDidCatch(error, errorInfo) {
    // Log to monitoring
  }
}

Retry with Backoff

async function retryWithBackoff<T>(fn, maxRetries = 3): Promise<T>

Best Practices

• User-friendly messages, no sensitive info
• Log all errors with context
• Integrate error monitoring (Sentry)
• Implement retry logic and circuit breakers
• Provide fallback values
• Test error cases

Recovery Strategies

1. Retry Logic – Exponential backoff
2. Circuit Breaker – Prevent cascade failures
3. Fallback Values – Graceful degradation

For complete exception filter implementations, custom exceptions, validation pipe setup, error boundaries, circuit breaker pattern, logging integration, and database/API error patterns, see: references/full-guide.md