Logging best practices

Skill secondsky/claude-skills/plugins/logging-best-practices/skills/logging-best-practices

Production-ready skills for Claude Code CLI - Cloudflare, React, Tailwind v4, and AI integrations

Install

npx -y skills add secondsky/claude-skills --skill logging-best-practices

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Structured logging with proper levels, context, PII handling, centralized aggregation. Use for application logging, log management integration, distributed tracing, or encountering log bloat, PII exposure, missing context errors.

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SKILL.md

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Logging Best Practices

Implement secure, structured logging with proper levels and context.

Log Levels

Level	Use For	Production
DEBUG	Detailed debugging	Off
INFO	Normal operations	On
WARN	Potential issues	On
ERROR	Errors with recovery	On
FATAL	Critical failures	On

Structured Logging (Winston)

const winston = require('winston');

const logger = winston.createLogger({
  level: process.env.LOG_LEVEL || 'info',
  format: winston.format.combine(
    winston.format.timestamp(),
    winston.format.json()
  ),
  defaultMeta: { service: 'api-service' },
  transports: [
    new winston.transports.Console(),
    new winston.transports.File({ filename: 'error.log', level: 'error' })
  ]
});

// Usage
logger.info('User logged in', { userId: '123', ip: '192.168.1.1' });
logger.error('Payment failed', { error: err.message, orderId: '456' });

Request Context

const { AsyncLocalStorage } = require('async_hooks');
const storage = new AsyncLocalStorage();

app.use((req, res, next) => {
  const context = {
    requestId: req.headers['x-request-id'] || uuid(),
    userId: req.user?.id
  };
  storage.run(context, next);
});

function log(level, message, meta = {}) {
  const context = storage.getStore() || {};
  logger.log(level, message, { ...context, ...meta });
}

PII Sanitization

const sensitiveFields = ['password', 'ssn', 'creditCard', 'token'];

function sanitize(obj) {
  const sanitized = { ...obj };
  for (const field of sensitiveFields) {
    if (sanitized[field]) sanitized[field] = '[REDACTED]';
  }
  if (sanitized.email) {
    sanitized.email = sanitized.email.replace(/(.{2}).*@/, '$1***@');
  }
  return sanitized;
}

Best Practices

Use structured JSON format
Include correlation IDs across services
Sanitize all PII before logging
Use async logging for performance
Implement log rotation
Never log at DEBUG in production

Additional Implementations

See references/advanced-logging.md for:

Python structlog setup
Go zap high-performance logging
ELK Stack integration
AWS CloudWatch configuration
OpenTelemetry tracing

Never Do

Log passwords or tokens
Use console.log in production
Log inside tight loops
Include stack traces for client errors