Logging in Go has come a long way. For years, the community relied on the simple standard log Copy package or turned to powerful third-party libraries like zap and zerolog .
With the introduction of log/slog in Go 1.21 , the language now has a native, high-performance, structured logging solution designed to be the new standard.
slog Copy isn’t just another logger; it’s a new foundation that provides a common API (the frontend) that separates logging logic from the final output, which is controlled by various logging implementations (the backend).
This guide will take you through slog Copy from its fundamentals to advanced patterns, showing you how to make logging a useful signal for observing your applications.
The log/slog Copy package is built around three core types: the Logger Copy , the Handler Copy , and the Record Copy . The Logger Copy is the frontend you’ll interact with, the Handler Copy is the backend that does the actual logging work, and the Record Copy is the data passed between them.
A Record Copy represents a single log event. It contains all the necessary information about the event including:
The time of the event.
The severity level ( INFO Copy , WARN Copy , etc.).
, , etc.). The log message.
All structured key-value attributes.
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