Log Levels

There are six levels, from most verbose to most critical. Internally they use priority 0–5 (see the API reference for the exact table).

Choosing a level

• trace / debug — local troubleshooting, high volume (often off in production).
• info — normal lifecycle events (started, completed).
• warn — something odd but the app continues.
• error / fatal — failures; fatal is reserved for the worst cases.

Filtering with minLevel

Only messages with severity ≥ minLevel are emitted. Example:

const log = createLogger('App', { minLevel: 'warn' });

log.info('startup');  // skipped — below `warn`
log.warn('slow');     // kept
log.error('failed');  // kept

Matrix

minLevel	trace	debug	info	warn	error	fatal
'trace'	✅	✅	✅	✅	✅	✅
'debug'	❌	✅	✅	✅	✅	✅
'info'	❌	❌	✅	✅	✅	✅
'warn'	❌	❌	❌	✅	✅	✅
'error'	❌	❌	❌	❌	✅	✅
'fatal'	❌	❌	❌	❌	❌	✅

Global + per-logger

configure({ minLevel }) and setGlobalLevel() set a global floor. The stricter of the global floor and each logger’s minLevel wins (so a logger created with minLevel: 'error' does not start logging at info when the global is trace). Details: Global configuration.

See also

• API: levels & environment defaults
• Environment & NODE_ENV
• Timing (time / timer.end logs at debug )