A production-ready, context-aware, structured logger for Go. JSON/logfmt/ECS/GCP formats, ANSI colors, child fields, async flushing, and pluggable sinks. Sensible defaults for dev and prod, plus security helpers (redaction, size limits, allowlist). See examples/ to copy-paste usage.

• Child loggers: With(fields) for persistent context
• Multiple formats: JSON, logfmt, ECS, GCP Cloud Logging, Console
• Message shaping: Msgf(), Err(err).Msg(), KV() helpers
• Dynamic levels: Runtime level changes with SetLevel()
• Smart defaults: TTY detection, NO_COLOR support

• Batching: Configurable batch sizes and timeouts
• Backpressure: Block, drop oldest, or sample strategies
• Zero-alloc: Buffer pooling with sync.Pool
• Atomic config: Thread-safe configuration updates

• Pluggable sinks: stdout, stderr, file, HTTP, with retry/backoff
• Circuit breakers: Automatic failure detection and recovery
• Spool to disk: Network outage resilience
• Crash-safe hooks: Isolated error handling

The following features are marked as experimental and may change in future versions:

• HTTPSink: HTTP endpoint logging with retry and circuit breaker support
• RetrySink: Exponential backoff with failure tracking
• CircuitBreakerSink: Failure windows, half-open probing, and state management
• SpoolSink: Disk persistence on failure and drain on recovery
• Metrics & Health: Real-time observability with Prometheus export
• PrometheusExporter: Metrics export functionality

These features are production-ready but may have API changes in future versions.

• PII redaction: Email, SSN, credit card, phone number patterns
• Secret scrubbing: Password, API key, token auto-masking
• Size limits: Configurable message truncation
• Schema allowlist: Field-level access control

• Prometheus metrics: logs_emitted_total, queue_depth, etc.
• Health checks: logger.Health() with diagnostics
• Self-diagnostics: Comprehensive system status

Get started by reading the usage examples in the examples/ package.

Running examples:

# Run all examples.
go test ./examples -count 1 -v
# Run specific example.
go test ./examples -count 1 -v -run Test_BasicLogging

export LOG_LEVEL=INFO
export LOG_FORMAT=json
export LOG_COLOR=true
export LOG_ASYNC_BUF=1000
export NO_COLOR=1 # Disable colors

Use the smart builder for environment-aware defaults:

// Automatically detects environment and applies appropriate defaults
smartLogger := logger.NewSmart(ctx, func(context.Context) *logger.ExtraData {
 return &logger.ExtraData{
 TraceID: "trace-123",
 SpanID: "span-456",
 }
})