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')