---

name: api-error-handling description: Implements standardized API error responses with proper status codes, logging, and user-friendly messages. Use when building production APIs, implementing error recovery patterns, or integrating error monitoring services.

API Error Handling

Implement robust error handling with standardized responses and proper logging.

Standard Error Response Format

Copy{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Invalid request parameters",
    "status": 400,
    "requestId": "req_abc123",
    "timestamp": "2025-01-15T10:30:00Z",
    "details": [
      { "field": "email", "message": "Invalid email format" }
    ]
  }
}

Error Class (Node.js)

Copyclass ApiError extends Error {
  constructor(code, message, status = 500, details = null) {
    super(message);
    this.code = code;
    this.status = status;
    this.details = details;
  }

  static badRequest(message, details) {
    return new ApiError('BAD_REQUEST', message, 400, details);
  }

  static notFound(resource) {
    return new ApiError('NOT_FOUND', `${resource} not found`, 404);
  }

  static unauthorized() {
    return new ApiError('UNAUTHORIZED', 'Authentication required', 401);
  }
}

// Global error handler
app.use((err, req, res, next) => {
  const status = err.status || 500;
  const response = {
    error: {
      code: err.code || 'INTERNAL_ERROR',
      message: status === 500 ? 'Internal server error' : err.message,
      status,
      requestId: req.id
    }
  };

  if (err.details) response.error.details = err.details;
  if (status >= 500) logger.error(err);

  res.status(status).json(response);
});

Circuit Breaker Pattern

Copyclass CircuitBreaker {
  constructor(threshold = 5, timeout = 30000) {
    this.failures = 0;
    this.threshold = threshold;
    this.timeout = timeout;
    this.state = 'CLOSED';
  }

  async call(fn) {
    if (this.state === 'OPEN') throw new Error('Circuit open');
    try {
      const result = await fn();
      this.failures = 0;
      return result;
    } catch (err) {
      this.failures++;
      if (this.failures >= this.threshold) {
        this.state = 'OPEN';
        setTimeout(() => this.state = 'HALF_OPEN', this.timeout);
      }
      throw err;
    }
  }
}

Additional Implementations

See references/python-flask.md for:

• Python Flask error handling with custom exceptions
• Circuit breaker with automatic recovery
• Retry with exponential backoff
• Sentry integration

Best Practices

• Use consistent error format across all endpoints
• Include request IDs for traceability
• Log errors at appropriate severity levels
• Never expose stack traces to clients
• Distinguish client errors (4xx) from server errors (5xx)
• Provide actionable error messages