Winston Logger - Quick Reference
When to Use This Skill
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Logging with multiple transports (file, console, HTTP)
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Structured logging with custom levels
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Automatic log file rotation
Deep Knowledge: Use mcp__documentation__fetch_docs with technology: winston for comprehensive documentation.
Basic Setup
npm install winston
Essential Patterns
Logger Base
import winston from 'winston';
const logger = winston.createLogger({ level: 'info', format: winston.format.combine( winston.format.timestamp(), winston.format.json() ), transports: [ new winston.transports.File({ filename: 'error.log', level: 'error' }), new winston.transports.File({ filename: 'combined.log' }), ], });
// Add console in development if (process.env.NODE_ENV !== 'production') { logger.add(new winston.transports.Console({ format: winston.format.simple(), })); }
Custom Format
const customFormat = winston.format.printf(({ level, message, timestamp, ...meta }) => {
return ${timestamp} [${level.toUpperCase()}]: ${message} ${Object.keys(meta).length ? JSON.stringify(meta) : ''};
});
const logger = winston.createLogger({ format: winston.format.combine( winston.format.timestamp(), customFormat ), transports: [new winston.transports.Console()], });
Child Logger
const childLogger = logger.child({ requestId: req.id, module: 'auth' }); childLogger.info('User authenticated', { userId: user.id });
Daily Rotate File
import DailyRotateFile from 'winston-daily-rotate-file';
const transport = new DailyRotateFile({ filename: 'logs/app-%DATE%.log', datePattern: 'YYYY-MM-DD', maxSize: '20m', maxFiles: '14d', });
logger.add(transport);
When NOT to Use This Skill
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High-performance APIs: Use Pino instead - 10x faster than Winston
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JSON-only logging: Pino is more optimized for structured JSON output
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Serverless/Lambda: Prefer simpler console logging or Pino for lower overhead
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Python/Java projects: Use language-specific logging frameworks
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Simple scripts: Built-in console is sufficient for basic debugging
Anti-Patterns
Anti-Pattern Why It's Bad Solution
Synchronous file logging Blocks event loop, degrades performance Use async transports with { stream: ... }
Logging objects without serialization Can log [Object] instead of data Use JSON.stringify() or Winston JSON format
No log rotation Disk fills up in production Use winston-daily-rotate-file
Logging in tight loops Overwhelms I/O, fills disks Add conditional logic or sample logs
String concatenation Always evaluated, even when disabled Use format strings: logger.info('User %s', userId)
Missing error stack traces Loses debugging context Use { error: err } or Winston error format
Quick Troubleshooting
Issue Cause Solution
Logs not appearing Wrong log level configured Check logger.level and transport levels
Performance degradation Synchronous file writes Use async transports or reduce log verbosity
Disk full No log rotation Configure winston-daily-rotate-file with maxFiles
[Object] in logs Improper object formatting Use winston.format.json() or winston.format.prettyPrint()
Duplicate logs Multiple transports to same destination Review transport configuration
Colors not showing Console transport missing colorize Add winston.format.colorize() to console transport