Pino Logging

Fastify uses Pino — a fast structured JSON logger with per-request child loggers and a pino-pretty transport for development.

4 min read Level 2/5 #fastify#logging#pino

What you'll learn

Enable the logger via Fastify factory options
Use app.log and request.log
Switch to pretty output during development

Fastify integrates Pino directly, so every app gets fast structured logging without extra setup.

Enabling the Logger

const app = Fastify({
  logger: {
    level: process.env.LOG_LEVEL ?? 'info',
  },
});

By default each request logs incoming request and request completed lines with reqId, method, URL, status, and response time.

App and Request Loggers

app.log.info({ version: '1.0.0' }, 'booting');

app.post('/login', async (req) => {
  req.log.info({ email: req.body.email }, 'login attempt');
  return { ok: true };
});

request.log is a child logger pre-bound with the reqId, so every line tied to that request is correlated.

Pretty Output in Dev

npm i -D pino-pretty

const app = Fastify({
  logger: {
    level: 'debug',
    transport:
      process.env.NODE_ENV !== 'production'
        ? { target: 'pino-pretty', options: { colorize: true } }
        : undefined,
  },
});

Production keeps raw JSON so log aggregators (Loki, Datadog, CloudWatch) can index every field.

Per-Route Log Level

You can tune verbosity for a single noisy route:

app.get('/healthz', { logLevel: 'warn' }, async () => ({ ok: true }));

Configuration & dotenv →