SKILL.md
Application Logging
Table of Contents
- [Overview](#overview)
- [When to Use](#when-to-use)
- [Quick Start](#quick-start)
- [Reference Guides](#reference-guides)
- [Best Practices](#best-practices)
Overview
Implement comprehensive structured logging with proper levels, context, and centralized aggregation for effective debugging and monitoring.
When to Use
- Application debugging
- Audit trail creation
- Performance analysis
- Compliance requirements
- Centralized log aggregation
Quick Start
Minimal working example:
// logger.js
const winston = require("winston");
const logFormat = winston.format.combine(
winston.format.timestamp({ format: "YYYY-MM-DD HH:mm:ss" }),
winston.format.errors({ stack: true }),
winston.format.json(),
);
const logger = winston.createLogger({
level: process.env.LOG_LEVEL || "info",
format: logFormat,
defaultMeta: {
service: "api-service",
environment: process.env.NODE_ENV || "development",
},
transports: [
new winston.transports.Console({
format: winston.format.combine(
winston.format.colorize(),
winston.format.simple(),
),
}),
new winston.transports.File({
filename: "logs/error.log",
// ... (see reference guides for full implementation)Reference Guides
Detailed implementations in the references/ directory:
| Guide | Contents |
|---|---|
| Node.js Structured Logging with Winston | Node.js Structured Logging with Winston |
| Express HTTP Request Logging | Express HTTP Request Logging |
| Python Structured Logging | Python Structured Logging |
| Flask Integration | Flask Integration |
| ELK Stack Setup | ELK Stack Setup |
| Logstash Configuration | Logstash Configuration |
Best Practices
✅ DO
- Use structured JSON logging
- Include request IDs for tracing
- Log at appropriate levels
- Add context to error logs
- Implement log rotation
- Use timestamps consistently
- Aggregate logs centrally
- Filter sensitive data
❌ DON'T
- Log passwords or secrets
- Log at INFO for every operation
- Use unstructured messages
- Ignore log storage limits
- Skip context information
- Log to stdout in production
- Create unbounded log files