zap
Blazing-fast structured logging library for Go from Uber. Provides two interfaces: Logger (zero-allocation, maximum performance) and SugaredLogger (more convenient, slightly slower). Outputs structured JSON logs ideal for log aggregation platforms (Datadog, ELK, Loki). 4-10x faster than other Go structured loggers.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Be careful not to log sensitive data (tokens, passwords, PII) in structured fields — all fields are exported to log sinks. No network calls — outputs to configured writers.
⚡ Reliability
Best When
You're building a production Go service or agent backend where logging performance and structured JSON output for log aggregation are requirements.
Avoid When
You just need simple log output in a tool or script — log.Printf from the standard library is simpler; zap's setup overhead isn't worth it for scripts.
Use Cases
- • Add high-performance structured logging to Go agent services with zero-allocation JSON output for log aggregation
- • Log agent tool calls, LLM API requests, and task completions with typed fields (String, Int, Duration) for searchability
- • Build production Go agent backends where logging overhead is a concern — zap adds <100ns per log statement
- • Output structured agent logs to stdout for container platforms (Docker, Kubernetes) that aggregate via fluentd/filebeat
- • Implement log sampling for high-volume Go agent operations to reduce log volume while maintaining visibility
Not For
- • Simple Go scripts or tools where fmt.Println or log.Printf is sufficient
- • Applications requiring human-readable console output without JSON — use zerolog or logrus for colored console output
- • Teams prioritizing API simplicity over performance — logrus has a more familiar API at the cost of some performance
Interface
Authentication
Local logging library — no authentication required.
Pricing
MIT license. Open-sourced by Uber Technologies.
Agent Metadata
Known Gotchas
- ⚠ zap.NewProduction() and zap.NewDevelopment() create loggers with different defaults — production uses JSON, development uses console format; always use production config in deployed agents
- ⚠ Logger is not goroutine-safe for configuration changes but is safe for concurrent logging — share a single *zap.Logger across goroutines; don't create per-request loggers
- ⚠ SugaredLogger's With() method returns a new SugaredLogger (not mutating) — always capture the returned logger; discarding the return value loses the added fields
- ⚠ Caller skip in zap.WithOptions(zap.AddCallerSkip(n)) must be set correctly when wrapping zap in your own logger helper — incorrect skip shows wrong file/line in logs
- ⚠ zap doesn't automatically log to stderr on panic/fatal — it logs to the configured core output; ensure sink handles fatal-level messages before process exit
- ⚠ Field types must match — passing a string to zap.Int() causes a build error; use zap.Any(key, value) for dynamic types when field type is unknown at compile time
Alternatives
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Scores are editorial opinions as of 2026-03-07.