Pino Logger - Quick Reference

When to Use This Skill

Structured logging in Node.js applications
High-performance logging
Integration with log aggregation systems

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: pino for comprehensive documentation.

Basic Setup

npm install pino pino-pretty

Essential Patterns

Logger Base

import pino from 'pino';

const logger = pino({
  level: process.env.LOG_LEVEL || 'info',
  transport: {
    target: 'pino-pretty',
    options: { colorize: true }
  }
});

logger.info('Server started');
logger.error({ err }, 'Failed to connect');

Child Logger

const childLogger = logger.child({
  module: 'auth',
  requestId: req.id
});

childLogger.info({ userId }, 'User authenticated');

Express Integration

import pinoHttp from 'pino-http';

app.use(pinoHttp({ logger }));

Fastify Integration

import Fastify from 'fastify';

const fastify = Fastify({
  logger: {
    level: 'info',
    transport: {
      target: 'pino-pretty'
    }
  }
});

Production Configuration

const logger = pino({
  level: 'info',
  formatters: {
    level: (label) => ({ level: label }),
  },
  timestamp: pino.stdTimeFunctions.isoTime,
  base: {
    pid: process.pid,
    hostname: os.hostname(),
  },
});

When NOT to Use This Skill

Complex multi-transport requirements: Winston offers more flexible transport system
Custom log formatting beyond JSON: Winston has more formatting options
Development-only logging: Built-in console is simpler for quick debugging
Python/Java projects: Use language-specific logging frameworks
Legacy apps expecting text logs: Pino is JSON-first, requires parsing tools

Anti-Patterns

Anti-Pattern	Why It's Bad	Solution
Using pino-pretty in production	2-3x performance penalty	Only use in development, raw JSON in prod
Logging large objects	Serialization overhead	Log only necessary fields
Synchronous logging	Defeats Pino's async advantage	Use default async mode, avoid `pino.final()`
Nested child loggers without cleanup	Memory leak over time	Reuse child loggers or clear references
Logging in hot paths without level check	Still has minimal overhead	Use `if (logger.isLevelEnabled('debug'))` for extreme cases
Mixing multiple logger instances	Inconsistent configuration	Create one base logger, use child loggers

Quick Troubleshooting

Issue	Cause	Solution
Unreadable JSON in console	No pretty-printer configured	Add `pino-pretty` transport for development
Performance slower than expected	pino-pretty enabled in production	Remove pretty-printer, use raw JSON
Missing logs	Level too high	Check `level` configuration matches environment
Context not included	Not using child logger	Use `logger.child({ context })` for request scoping
Logs not flushing on exit	Async logging buffer	Use `pino.final()` or flush on SIGTERM
Extra fields not appearing	Incorrect syntax	Use object as first param: `logger.info({ field }, 'msg')`