slog – Structured Logging for Go

A clean, idiomatic logger with syslog-style levels and a special Crazy dev-only level.

Features

• Syslog-style log levels: emerg, alert, crit, error, warn, notice, info, debug
• Dev-only Crazy log level, only included with -tags dev
• Log level filtering: set the minimum level to log
• Simple API: use slog.Info(...), slog.Error(...), etc.

Installation

go get github.com/TenforwardAB/slog

Usage

import "github.com/TenforwardAB/slog"

func main() {
	slog.SetLevel("info") // or "debug", "warn", etc.

	slog.Info("Application started")
	slog.Warn("This is a warning")
	slog.Crazy("This is a dev-only log") // Only works with -tags dev
}

Supported log levels

Name	Alias(es)	Severity (low → high)	Description
debug	–	0	Detailed internal debugging messages
info	–	1	General system information
notice	–	2	Significant but expected events
warn	warning	3	Potential problems
error	–	4	Errors that require attention
crit	critical	5	Critical conditions that may crash the system
alert	–	6	Immediate action needed
emerg	emergency	7	System is unusable
crazy	dev only	0	Experimental/dev-only logs (only with -tags dev)

Invalid log levels

If you call:

slog.SetLevel("banana")

You’ll get:

invalid log level: banana

You can handle this:

if err := slog.SetLevel(cfg.LogLevel); err != nil {
	log.Printf("invalid log level %q, falling back to info", cfg.LogLevel)
	slog.SetLevel(slog.LevelInfo)
}

Dev-only logs

The Crazy() method is only compiled in if you build with:

go run -tags dev examples/main.go

In production, the Crazy() method becomes a no-op.

Example

See examples/main.go for a complete example.