Conciseness

The body is dominated by executable Swift with brief, useful framing, but contains minor over-explanation of concepts Claude already knows (e.g., 'AVAudioSession coordinates app audio with the system audio subsystem' and 'AVAudioEngine coordinates a graph of AVAudioNode instances'). This matches the 4 anchor — efficient with a few trimmable sentences — rather than the 5 anchor where every token earns its place.

Actionability

Four complete, executable Swift code blocks cover the common cases (session configuration, async interruption handling, playback graph, microphone tap), reinforced by concrete directives like 'Always call removeTap(onBus:) first' and pausing on '.oldDeviceUnavailable'. Code is copy-paste ready with real class implementations, matching the 5 anchor.

Workflow Clarity

Sections are clearly sequenced (session configuration → notifications → engine graph → taps) and the Review Checklist provides verification checkpoints, but there are no explicit error-recovery feedback loops. This fits the 4 anchor ('clear sequence with most checkpoints present; minor validation gaps') rather than 5, which requires explicit feedback loops; it is above 3 because checkpoints are present rather than missing.

Progressive Disclosure

The SKILL.md is a lean overview with a Contents TOC, and advanced material (multi-track mixer graphs, real-time effects, format conversion, permission/recording) is appropriately split into references/audio-engine-patterns.md — a real file that is well-signaled in the References section with a descriptive annotation and is one level deep with no nested references.

Specificity

The description enumerates multiple concrete, API-level actions — 'Configure AVAudioSession categories, modes, route changes, interruptions' and 'build low-latency AVAudioEngine node graphs for recording, mixing, and audio processing' — giving comprehensive coverage of both session and engine concerns. It exceeds the 4 anchor because the action list is broad and specific rather than having notable gaps.

Completeness

The 'what' is clearly and concretely stated, but there is no 'Use when...' clause or equivalent explicit trigger guidance; 'in iOS and iPadOS apps' only weakly implies when to use it. Per the judging guidelines, a missing trigger clause caps completeness at 3, and the description is not at 4 because the 'when' is absent rather than merely imprecise.

Trigger Term Quality

Includes natural terms users would say such as 'AVAudioSession', 'AVAudioEngine', 'recording', 'mixing', 'route changes', 'interruptions', and 'iOS'. A few common natural terms are missing (e.g., 'microphone', 'playback', 'audio session'), which matches the 4 anchor rather than the comprehensive 5 anchor.

Distinctiveness Conflict Risk

The description occupies a clear niche — AVFoundation audio on iOS/iPadOS — with distinct framework-specific triggers (AVAudioSession, AVAudioEngine) that are unlikely to fire for unrelated skills. It matches the 5 anchor for minimal conflict risk.