Bunyan
Structured JSON logging library for Node.js. Bunyan emits log records as newline-delimited JSON, includes a CLI tool (bunyan) for pretty-printing and filtering, supports child loggers with inherited context, and uses Node.js streams for multi-destination output. One of the original Node.js structured logging libraries — now largely superseded by Pino for performance but still found in many production codebases.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Unmaintained since 2017 — security vulnerabilities possible. JSON logging means sensitive data may appear in logs if serializers don't redact it. Audit before production use.
⚡ Reliability
Best When
Maintaining an existing Bunyan-based codebase or when Bunyan's child logger API and stream architecture match existing infrastructure.
Avoid When
Starting a new project — use Pino for equivalent structured JSON logging with significantly better performance.
Use Cases
- • Log structured agent operations as JSON for ingestion into Elasticsearch, Splunk, or Datadog without log parsing overhead
- • Create child loggers with inherited context (requestId, agentId) using log.child() to maintain context through async operation chains
- • Route agent logs to multiple destinations (file, stdout, error service) using Bunyan streams with independent log level thresholds
- • Filter production logs in development using Bunyan CLI (bunyan -l warn) to show only high-priority events from JSON log files
- • Add serializers to standardize how objects (errors, HTTP requests) are logged across all agent log entries
Not For
- • New Node.js projects — Pino is 5-10x faster than Bunyan and actively maintained; use Pino for new projects
- • Browser logging — Bunyan is Node.js only; use browser-appropriate loggers for frontend
- • TypeScript-first projects — Pino has better TypeScript support and active development
Interface
Authentication
No authentication — local logging library.
Pricing
Bunyan is open source and free. Note: the library has not had active development since 2017.
Agent Metadata
Known Gotchas
- ⚠ Bunyan is effectively unmaintained (last release 2017) — security vulnerabilities may not be patched; audit dependencies and consider migrating to Pino
- ⚠ Bunyan uses synchronous write for file streams which blocks the event loop at high log volumes — Pino's async transport is significantly better for high-throughput agents
- ⚠ RingBuffer stream for in-memory log buffering has no size limit by default — in long-running agents set an explicit ringBuffer limit to prevent memory growth
- ⚠ Circular reference in logged objects causes JSON serialization to throw — use serializers to normalize objects before logging
- ⚠ Bunyan level numbers (10=trace, 20=debug, 30=info) differ from other logging frameworks — don't compare level numbers across different logging libraries
- ⚠ Child logger field names override parent fields silently — if child and parent have the same field, child value wins without warning; be careful with requestId inheritance
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Bunyan.
Scores are editorial opinions as of 2026-03-06.