How to implement logging in Express.js (Morgan, Winston)?

Logging in Express.js

Proper logging is essential for debugging, monitoring, and auditing production applications. Express uses two main logging libraries: Morgan for HTTP request logging and Winston for application-level logging.

Morgan — HTTP Request Logger

Morgan logs every incoming HTTP request:

bash

npm install morgan

const morgan = require('morgan');

// Predefined formats
app.use(morgan('dev'));      // Colored output for development
app.use(morgan('combined')); // Apache-style for production
app.use(morgan('tiny'));     // Minimal output

Format examples:

// dev format:
GET /api/users 200 12.345 ms - 250

// combined format:
::1 - - [01/Mar/2026:10:00:00 +0000] "GET /api/users HTTP/1.1" 200 250

// tiny format:
GET /api/users 200 250 - 12.345 ms

Custom format:

morgan.token('body', (req) => JSON.stringify(req.body));

app.use(morgan(':method :url :status :response-time ms - :body'));

Log to file:

const fs = require('fs');
const path = require('path');

const accessLogStream = fs.createWriteStream(
  path.join(__dirname, 'access.log'),
  { flags: 'a' }
);

app.use(morgan('combined', { stream: accessLogStream }));

Winston — Application Logger

Winston is a versatile logging library with multiple transports:

bash

npm install winston

const winston = require('winston');

const logger = winston.createLogger({
  level: 'info',
  format: winston.format.combine(
    winston.format.timestamp(),
    winston.format.errors({ stack: true }),
    winston.format.json()
  ),
  defaultMeta: { service: 'my-api' },
  transports: [
    new winston.transports.File({ filename: 'logs/error.log', level: 'error' }),
    new winston.transports.File({ filename: 'logs/combined.log' })
  ]
});

// Add console in development
if (process.env.NODE_ENV !== 'production') {
  logger.add(new winston.transports.Console({
    format: winston.format.combine(
      winston.format.colorize(),
      winston.format.simple()
    )
  }));
}

Usage:

logger.info('Server started', { port: 3000 });
logger.warn('Slow query detected', { query: 'SELECT...', duration: 5000 });
logger.error('Database connection failed', { error: err.message });

Combining Morgan + Winston

const morganStream = {
  write: (message) => logger.http(message.trim())
};

app.use(morgan('combined', { stream: morganStream }));

Log Levels

Level	Priority	Use Case
`error`	0	Application errors
`warn`	1	Deprecations, slow queries
`info`	2	Key events (startup, shutdown)
`http`	3	HTTP requests
`debug`	4	Detailed debugging
`verbose`	5	Even more detail
`silly`	6	Everything

Best Practices

Practice	Description
Structured logging	Use JSON format for machine parsing
Request ID	Add unique ID to trace requests across logs
Don't log secrets	Filter passwords, tokens, credit cards
Log rotation	Use `winston-daily-rotate-file`
Centralized logging	Ship to ELK Stack, Datadog, or CloudWatch
Different levels per env	`debug` in dev, `info` in prod

// Request ID middleware
const { v4: uuid } = require('uuid');

app.use((req, res, next) => {
  req.requestId = req.headers['x-request-id'] || uuid();
  res.setHeader('x-request-id', req.requestId);
  next();
});

Production tip: Always use structured JSON logging. Attach request IDs for tracing. Ship logs to a centralized service. Never log sensitive data like passwords, tokens, or personal information.

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