Instruction file imported from ncosentino/needlr (.github/instructions/genesis/go/logging.instructions.md). Copyright stays with the author.

Go logging

Use the standard library log/slog for structured logging. It needs no external dependency and is the current ecosystem default for command-line tools.

logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
	Level: slog.LevelInfo,
}))
slog.SetDefault(logger)

slog.Info("starting", "addr", addr, "version", version)

Rules:

• Log to stderr, not stdout — stdout is reserved for the command's actual output so it can be piped and parsed.
• Use structured key/value attributes (slog.Info("msg", "key", value)); do not format variable data into the message string.
• Use lowercase, constant message strings and camelCase attribute keys.
• Do not log and return the same error — wrap and return it, and let the single top-level handler decide whether to print it.
• Use fmt.Fprintln(cmd.OutOrStdout(), ...) for user-facing command output; reserve slog for diagnostics.