Conciseness

The body is largely lean (DO/DON'T lists, tight code snippets), but the Quick Start Guide bullets duplicate the References section descriptions verbatim (e.g. 'Creating new error types or error enums' appears twice), and the HashQL rationale lists diagnostic capabilities (spans, labels, severity levels) Claude already knows. It fits the 'efficient with minor trim opportunities' anchor rather than score 5's 'every token earns its place'.

Actionability

Concrete, copy-paste-ready Rust snippets with the required imports cover the common cases — creating an error, propagating with change_context/attach, and lazy attach_with — alongside executable rules like 'Import Error from core::error:: (not std::error::)' and 'Import ResultExt as _'. This is not score 4 because the examples span the common cases rather than leaving gaps.

Workflow Clarity

For a reference-routing skill, the navigation workflow is unambiguous: 'Choose the reference that matches your current task' with per-reference 'Use when' clauses, plus a location table cleanly routing the HashQL exception to the diagnostics skill. No destructive or batch operations exist, so no validation cap applies.

Progressive Disclosure

The body is a genuine overview: three well-signaled references (defining-errors.md, propagating-errors.md, documenting-errors.md) that all exist and stay one level deep (they only cross-link to siblings), with detail appropriately split out and quick patterns kept inline. This is not score 4 because the split and signaling are essentially ideal.

Specificity

The description names the domain and five concrete actions with real API names: 'defining custom errors, propagating errors with change_context, adding context with attach, implementing Error trait, documenting error conditions'. This matches the comprehensive-coverage anchor; it is not score 4 because there are no notable gaps in the actions listed.

Completeness

It explicitly answers both what ('HASH error handling patterns using error-stack crate') and when ('Use when working with Result types, Report types, defining custom errors...') with concrete trigger phrases, in third-person voice.

Trigger Term Quality

It includes the natural terms a Rust developer would actually say: 'Result types', 'Report types', 'custom errors', 'propagating errors', 'Error trait', 'documenting error conditions', 'Rust code'. Coverage is comprehensive for this domain rather than merely good with a few missing terms.

Distinctiveness Conflict Risk

It carves out a clear niche (error-stack patterns in the HASH codebase) with distinct, crate-specific triggers, minimizing risk of firing for unrelated skills.