Blog / Standard Library

slog Records and levels

April 2, 2026

Yesterday we saw that slog uses handlers to process/record logs. But what exactly does it process? Records!

Overview

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A log record consists of a time, a level, a message, and a set of key-value pairs, where the keys are strings and the values may be of any type. As an example,

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

creates a record containing the time of the call, a level of Info, the message “hello”, and a single pair with key “count” and value 3.

When you use the log/slog package, you’re basically building records by (usually) calling level-specific methods, passing a message, and potentially key/value/value pairs. This record is then what’s passed to the handler(s) you’ve configured. The handler(s) then typically format the record as plain text, as JSON, or to send to your cloud logging API.

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Related Content

Working with Records

In my experience, it’s rare you’ll need to worry about slog Records, unless you’re writing a Handler, or some kind of middleware/transform. But even if you never need to manipulate a Record directly, understanding the concept can be useful. Working with Records Sometimes a Handler will need to modify a Record before passing it on to another Handler or backend. A Record contains a mixture of simple public fields (e.g. Time, Level, Message) and hidden fields that refer to state (such as attributes) indirectly.

slog Handler methods

slog.Handler is an interface type. We’re going to look at each method on that interface in turn. Understanding these methods is valuable if you’re ever implementing your own handler. If you’re only using slog to produce logs using existing handlers, you could skip this part… though maybe you’ll learn something interesting anyway! type Handler type Handler interface { // Enabled reports whether the handler handles records at the given level. // The handler ignores records whose level is lower.

Attribute equality

func (Attr) Equal func (a Attr) Equal(b Attr) bool Equal reports whether a and b have equal keys and values. That’s a pretty obvious, and opaque statement. How is equality determined? We have to look at the source to determine: func (a Attr) Equal(b Attr) bool { return a.Key == b.Key && a.Value.Equal(b.Value) } Okay, so it returns true if the keys are equal (that’s simple—they’re just strings) AND if the values are equal.

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