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') |
