Agent skill
logging-best-practices
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.
Install this agent skill to your Project
npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/other/other/logging-best-practices
SKILL.md
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
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