log/slog ships with two default handlers: the TextHandler and the JSONHandler.

Overview

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For more control over the output format, create a logger with a different handler. This statement uses New to create a new logger with a TextHandler that writes structured records in text form to standard error:

logger := slog.New(slog.NewTextHandler(os.Stderr, nil))

TextHandler output is a sequence of key=value pairs, easily and unambiguously parsed by machine. This statement:

logger.Info("hello", "count", 3)

produces this output:

time=2022-11-08T15:28:26.000-05:00 level=INFO msg=hello count=3

The package also provides JSONHandler, whose output is line-delimited JSON:

logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
logger.Info("hello", "count", 3)

produces this output:

{"time":"2022-11-08T15:28:26.000000000-05:00","level":"INFO","msg":"hello","count":3}

(There’s actually a third, the MultiHandler, that fans out logs to multiple handlers). You can also use a custom handler you’ve built, or one of many third-party library handlers out there in the wild…