Blog / Standard Library

Values

May 6, 2026

TIL Logger.LogAttrs is a thing! But what is that thing??

Yesterday I mentioned that using an slog.Attr can be marginally more efficient than using naked key/value pairs in a log call. While true, that glosses over what is likely to be a much more impactful performance consideration in certain applications…

Attrs and Values

…

The value part of an Attr is a type called Value. Like an [any], a Value can hold any Go value, but it can represent typical values, including all numbers and strings, without an allocation.

For the most efficient log output, use Logger.LogAttrs. It is similar to Logger.Log but accepts only Attrs, not alternating keys and values; this allows it, too, to avoid allocation.

The call

logger.LogAttrs(ctx, slog.LevelInfo, "hello", slog.Int("count", 3))

is the most efficient way to achieve the same output as

slog.InfoContext(ctx, "hello", "count", 3)

So by using an slog.Attr and passing it to the LogAttrs method of the logger, rather than the much more convenient level-based methods (Info, Error, etc), you can avoid an extra memory allocation per attribute.

For many applications this won’t matter much. But there are applications where constructing and streaming logs adds a significant burden to the garbage collector. If this describes your application, consider using the less convenient LogAttrs—at least in hot paths.

Share this

Direct to your inbox, daily. I respect your privacy .

Unsure? Browse the archive .

Related Content

Attrs

We’ve been talking about key/value pairs. The log/slog package has a name for these: Attr (short for “attribute”). And there’s more than one way to build an attribute: Attrs and Values An Attr is a key-value pair. The Logger output methods accept Attrs as well as alternating keys and values. The statement slog.Info("hello", slog.Int("count", 3)) behaves the same as slog.Info("hello", "count", 3) There are convenience constructors for Attr such as Int, String, and Bool for common types, as well as the function Any for constructing Attrs of any type.

Contexts

[**Idiomatic Testing in Go**](/idiomatic-testing/) starts TOMORROW! My my, how time flies! There are still a few seats available, and there’s still time to sign up. Learn how to get the most out of the tests in your Go app! One feature I often see overlooked capability of the log/slog package, is to extract log key/value pairs from context: Contexts Some handlers may wish to include information from the context.Context that is available at the call site.

More with Groups

Organizing log key/value pairs by group is a nice way to organize your logging data, but what about organizing the way your application groups data? Maybe you want all logs created by a particular code path to be grouped together. How can you accomplish this? Enter WithGroup… Groups … Use Logger.WithGroup to qualify all of a Logger’s output with a group name. Calling WithGroup on a Logger results in a new Logger with the same Handler as the original, but with all its attributes qualified by the group name.

Get daily content like this in your inbox!

Subscribe