Blog / Standard Library

slog.Group

July 9, 2026

The one Attr constructor not yet covered:

func Group

func Group(key string, args ...any) Attr

Group returns an Attr for a Group Value. The first argument is the key; the remaining arguments are converted to Attrs as in Logger.Log.

Use Group to collect several key-value pairs under a single key on a log line, or as the result of LogValue in order to log a single value as multiple Attrs.

Groups are conceptually simple. They’re how we nest log attributes under a common key, as we can see in the inline example:

logger.Info("finished",
		slog.Group("req",
			slog.String("method", r.Method),
			slog.String("url", r.URL.String())),
		slog.Int("status", http.StatusOK),
		slog.Duration("duration", time.Second))

For the default TextHandler, groups are logged with the full key path in dot-separated notation:

level=INFO msg=finished req.method=GET req.url=localhost status=200 duration=1s

For the JSONHandler, they’re logged as inline JSON objects:

{"level":"INFO","msg":"finished","req":{"method":"GET","url":"localhost"},"status":200,"duration":1000000000}
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Handler configuration

The default slog handlers are quite configurable. Overview … Both TextHandler and JSONHandler can be configured with HandlerOptions. There are options for setting the minimum level (see Levels, below), displaying the source file and line of the log call, and modifying attributes before they are logged. While HandlerOptions only exposes three fields: AddSource bool Level Leveler ReplaceAttr func(groups []string, a Attr) Attr The last one provides an immense amount of flexibility, letting you filter, replace, or augment log key/value pairs as they are processed.

Chosing an slog handler

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slog.GroupAttrs

Last time we looked at slog.Group, which accepts the variadic ...any as arguments. But there’s also a version that accepts slog.Attr values: func GroupAttrs func GroupAttrs(key string, attrs ...Attr) Attr GroupAttrs returns an Attr for a Group Value consisting of the given Attrs. GroupAttrs is a more efficient version of Group that accepts only Attr values. But notice there’s no mixed form of this, like there is for the standard logging functions.

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