Log Level Comparator
Compare log levels across 7 popular logging frameworks — Winston, Pino, Python, Log4j, syslog, Go slog, and Ruby Logger. Visual severity mapping table included.
Severity Mapping Table
| Severity | Description | Winston | Pino | Python | Log4j | Syslog | Go |
|---|---|---|---|---|---|---|---|
| Fatal / Emergency | System unusable — process crashes | error (highest) | fatal | CRITICAL | FATAL | EMERG/ALERT | ERROR |
| Error | Operation failed, needs attention | error | error | ERROR | ERROR | ERR | ERROR |
| Warning | Unexpected behavior, still working | warn | warn | WARNING | WARN | WARNING | WARN |
| Info | Normal events, key milestones | info | info | INFO | INFO | NOTICE/INFO | INFO |
| Debug | Diagnostic details, dev use | debug/verbose | debug | DEBUG | DEBUG | DEBUG | DEBUG |
| Trace / Verbose | Every detail, very noisy | silly | trace | — | TRACE | — | — |
Framework Level Hierarchies
Winston (Node.js)
Default Winston levels (npm log levels)
Pino (Node.js)
Pino fast JSON logger
Python logging
Python standard library logging module
Log4j / SLF4J (Java)
Log4j, Log4j2, SLF4J, Logback
Syslog (RFC 5424)
Linux syslog, RFC 5424 severity levels
Go (slog, zerolog)
Go standard slog, zerolog, zap
Ruby Logger
Ruby stdlib Logger, Rails logger
Quick Reference: Setting Log Levels
# Winston (Node.js)
const logger = winston.createLogger({
level: process.env.LOG_LEVEL || 'info',
});
# Python
import logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)
# Pino (Node.js)
const log = pino({ level: 'info' });
log.info('message')
# Go slog
slog.SetLogLoggerLevel(slog.LevelInfo)
slog.Info("message", "key", value)
Frequently Asked Questions
Why do different logging frameworks use different level names?▼
Logging frameworks evolved independently across languages and ecosystems. Winston uses error/warn/info/http/verbose/debug/silly. Python uses CRITICAL/ERROR/WARNING/INFO/DEBUG. Log4j uses FATAL/ERROR/WARN/INFO/DEBUG/TRACE. They're conceptually similar but the names differ — this tool maps equivalents.
What is the lowest log level I should use in production?▼
Most production apps use INFO or WARN as the minimum level. DEBUG and TRACE/VERBOSE are too noisy for production and may expose sensitive data. Use environment variables to control the level: LOG_LEVEL=info. Enable DEBUG only during debugging sessions.
What is the syslog RFC 5424 severity scale?▼
Syslog defines 8 severities (0-7): EMERGENCY(0), ALERT(1), CRITICAL(2), ERROR(3), WARNING(4), NOTICE(5), INFORMATIONAL(6), DEBUG(7). Most application logging frameworks map to a subset of these. Syslog is used in Linux systems, network devices, and cloud logging services.
What does log level filtering mean?▼
Setting a minimum log level means only logs at that level or higher severity are emitted. If you set level=WARN, then DEBUG and INFO messages are suppressed. Lower numeric values mean higher severity (syslog convention), but most frameworks use higher numbers = more verbose.
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