Logging with slog

Canonical guidance

• prefer structured keys over free-form concatenated log lines
• attach stable request or job context with With
• keep handler setup in a narrow composition layer

Use when

• service logs
• request tracing context
• machine-consumable log pipelines

Avoid

• interpolated blob strings with no stable fields
• repeating the same attributes at every call site
• hiding logger construction deep inside business logic

Preferred pattern

logger := slog.New(slog.NewJSONHandler(os.Stdout, nil)).With(
	slog.String("service", "api"),
)

logger.Info("request complete", slog.Int("status", http.StatusOK))

Anti-pattern

• unstructured printf logs in code paths that need machine-readable diagnostics

Explanation: This anti-pattern is tempting because printf is fast to type, but it throws away the structured context operators depend on.

Why

• structured logs are easier to query, aggregate, and correlate