Mastering Structured Logging in Go 1.21: A Deep Dive Into slog

2025-12-20 21:18:51

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Why Go Needed slog in the Standard Library

For over a decade, Go’s log package handled basic logging duties just fine. But as systems grew more complex and observability became critical, developers increasingly turned to third-party solutions. The ecosystem responded with powerful alternatives—logrus alone is trusted by over 100,000 packages. Yet this fragmentation created a problem: large applications ended up bundling multiple logging packages, each with different configurations and output formats, making centralized log analysis nearly impossible.

The Go team recognized that structured logging consistently ranked at the top of community priorities. Instead of picking a winner among competing packages, they chose a different path: bring structured logging into the standard library as a common framework. This wouldn’t replace existing solutions, but rather give them a shared backend to interoperate seamlessly.

How slog Works: From Basic Calls to Custom Handlers

At its core, slog keeps things simple. A basic log message is a one-liner:

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