OSLog Logging & Observability

Structured logging, performance tracing, and production telemetry on Apple platforms — three layers: Logger/OSLog (what happened), OSSignposter (how long it took), MetricKit (how the fleet behaves). The full API reference — setup, levels, the privacy model, viewing logs, signpost intervals, MetricKit payloads — lives in references/guide.md. This file is the decision and discipline layer: read it first, open the guide for specifics.

Dials

Set these explicitly at the start; they change what "correct" means.

1. LEVEL — notice-baseline (default; .notice+ for anything you'd want after a field failure, .debug/.info for dev-only trace) · debug-verbose (heavy .debug tracing while actively debugging a path) · errors-only (terse libraries/hot paths — only .error/.fault).
2. PRIVACY — default-private (default; every interpolated value is <private>, you opt specific non-PII values into .public) · explicit-public (a logging subsystem where most values are deliberately .public — still never PII).
3. SIGNALS — logs (Logger only) · logs+signposts (add OSSignposter intervals for latency-sensitive paths) · logs+metrickit (also subscribe to MetricKit for field metrics + crash/hang diagnostics).

When to use

Adding, reviewing, or cleaning up any logging, performance instrumentation, or production-observability code on Apple platforms — including ripping out print()/NSLog, choosing log levels, getting the privacy redaction right, timing a slow path, or wiring up MetricKit. If the task is purely reading logs for a bug (not writing logging code), this still applies for the OSLogStore / log CLI section.

Core rules