slog as the logger, stdlib only

byob-logging.1 logging

Problem: picking a logging library (logrus, zap, zerolog) locks the whole tool into that library's API, handler model, performance envelope, and dependency footprint. Migrating later means touching every log call site. And third-party loggers drift in and out of maintenance while stdlib does not.

Idea: use log/slog from the standard library (Go 1.21+). It ships with TextHandler and JSONHandler, has a pluggable Handler interface for custom backends (redaction, routing, testing), supports LogAttrs for a zero-alloc hot path, and composes with context.Context via slog.InfoContext. No extra dependency, no migration risk, and the API is small enough to learn in an afternoon.

Tradeoffs: slog's ecosystem of pre-built handlers (OTLP, Sentry, file rotation) is thinner than logrus's. You'll write the occasional custom handler — but the Handler interface is four methods, so that's a weekend project, not a rewrite.

Design

import "log/slog"

// Root handler, wired to IOStreams.ErrOut (see byob-iostreams.3).
h := slog.NewTextHandler(f.IOStreams.ErrOut, &slog.HandlerOptions{
    Level: slog.LevelWarn, // quiet by default; -v/-vv raises it
})
logger := slog.New(h)
slog.SetDefault(logger)

// In command code:
slog.InfoContext(ctx, "fetching items", "count", len(ids), "host", cfg.Host)