Winston
Universal logging library for Node.js with support for multiple transports (console, file, HTTP, stream), log levels, custom formatters, and structured JSON logging. The most widely used Node.js logging library — supports async transports, log rotation, metadata, and custom transports. Pluggable transport system enables writing to console, files, databases, or external services simultaneously.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
MIT licensed. Logging sensitive data is developer responsibility — avoid logging credentials/PII. Transport-level authentication configured per transport. No remote calls unless using HTTP transport.
⚡ Reliability
Best When
You need a flexible, battle-tested logging solution with multiple simultaneous transports, custom formatters, and rich ecosystem of plugins for Node.js services.
Avoid When
You're optimizing for maximum logging throughput or want the most modern structured logging approach — pino is faster and more focused.
Use Cases
- • Add structured JSON logging to Node.js agent services with consistent metadata fields (requestId, userId, sessionId)
- • Route logs to multiple destinations simultaneously — console for development, file for production, external service for aggregation
- • Implement log-level-based filtering in agent services — debug logs in development, warn/error only in production
- • Create child loggers with bound metadata for request-scoped logging in agent API servers
- • Build custom transports to route agent logs to specialized sinks (Datadog, CloudWatch, Elasticsearch)
Not For
- • High-performance logging at extreme throughput — pino is 5-10x faster; use pino for performance-critical applications
- • Browser logging — Winston is Node.js only; use browser-native console or loglevel for browser
- • Structured log streaming — pino's newline-delimited JSON and pino-pretty pipeline is more modern and faster
Interface
Authentication
Local library — no authentication required. MIT licensed. External transport authentication configured per transport.
Pricing
MIT licensed. Zero cost.
Agent Metadata
Known Gotchas
- ⚠ Must handle transport 'error' events or process will crash: logger.on('error', (err) => { /* handle */ }) — missing error handlers cause unhandled rejections
- ⚠ Child loggers inherit parent transports — logger.child({ requestId: '123' }) creates logger with added metadata fields for request-scoped logging
- ⚠ JSON format requires winston.format.json() in formatters array — default format is custom text, not JSON; add format.combine(format.timestamp(), format.json()) for structured logging
- ⚠ File transport does NOT do log rotation by default — use winston-daily-rotate-file package for production log rotation
- ⚠ Log levels are numeric priority — higher number = lower priority: error(0), warn(1), info(2), http(3), verbose(4), debug(5), silly(6); set level to control minimum logged
- ⚠ Silent mode (silent: true) suppresses all output — useful for tests but easy to accidentally leave enabled
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Winston.
Scores are editorial opinions as of 2026-03-06.