Agent Skills: Application Logging

Application Logging

Table of Contents

• Overview
• When to Use
• Quick Start
• Reference Guides
• 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