Skill authoring patterns

Skill Authoring Patterns (Apple/Swift catalog layer)

This is a thin complement, not a replacement. For the general discipline of writing a skill — whether a skill should exist at all, the test-first / RED-GREEN loop, matching the guidance form to the failure mode, and word-count budgets — use superpowers:writing-skills first. This skill adds only what is specific to this catalog and to Apple/Swift framework skills: how to word descriptions so an agent routes to the right framework skill, the section conventions we standardize on, and how we review skills.

When to invoke

• Writing a new SKILL.md for this repo (especially an Apple/Swift framework skill).
• Reviewing / CR-ing a skill for invocation precision and execution quality.
• A skill's description routes wrong (or over-fires); you're rewording it.
• A skill grew long and you're deciding what to move into references/.
• Choosing a new skill's name and granularity.

Scope

This skill owns the catalog-specific and Apple/Swift-specific authoring conventions below. It does not own: the decision to create a skill, test-first skill development, or general prose-economy rules — route those to superpowers:writing-skills. Distribution/packaging (plugin vs marketplace, discovery) → claude-skill-plugin-packaging.

Description as a precision router

The description is the only part of a skill that stays in the model's context by default (the body loads when the skill is invoked, and the description is length-capped). So spend its words on routing, not summary.

• Verb-anchored to observable intent: "Resolve Swift 6 concurrency errors…", "Audit SwiftUI runtime performance…".
• Embed the framework symbols / APIs that should trigger it — Sendable, @MainActor, MetricKit, AccessibilityFocusState. This is the highest-leverage delta for framework skills: an agent routing on "I'm getting a Sendable error" only lands here if Sendable is in the description.
• Chain trigger scenarios as a short list ("Use when … ; when … ; when …").
• Add a negative boundary when over-firing is a real risk (e.g. "discussing screens" vs "generate a mockup") — name when NOT to fire.
• Routing is the model's judgment, not literal string matching — write for a reader deciding "is this my situation?", not for a regex.

BAD:  description: Helps with accessibility.
GOOD: description: VoiceOver / Dynamic Type / touch-target implementation for SwiftUI & UIKit.
      Use when adding or auditing user-facing UI; when asked "make this accessible" / "VoiceOver
      doesn't read this" / "does this pass WCAG"; before an App Review a11y pass. Covers
      accessibilityLabel/value/hint/traits, Dynamic Type + minimumScaleFactor, 44pt targets.
      Does NOT cover deep Rotor/Focus APIs — see <sibling>.

Section conventions we standardize

Order the middle by the topic's pedagogy, but keep these conventions:

• ## Rationale — why this default was chosen. Unique to this catalog; keep it.
• ## Deviation considerations — when to override the default, and the cost. Also ours; keep it. (Example: "Drop to iOS 17 when targeting education devices — you lose full Observation behaviour." This heading is the catalog-wide form — most first-party skills use it.)
• ## Common Mistakes — concrete, anti-pattern-named items ("Using DateFormatter() in body"), as many as are real — do not pad to a number. For new skills; most pre-existing skills express this as inline anti-pattern sections instead and are not retrofitted.
• ## Review Checklist — a - [ ] list at the end, runnable top-to-bottom. For new skills; older skills use a prose ## Verification checklist and are not retrofitted.
• ## Related skills — siblings by name.

Use a scope-boundary line in the body wherever a sibling is close ("owns X; does NOT own Y → route to <sibling>") — this is what stops two framework skills both claiming the same request.

Skeleton (assembled)

---
name: <kebab-matches-folder>
description: <precision router — see above>
---
# <Title>
<1-paragraph scope: what it implements/reviews + target version>
## When to invoke
## Scope            ← what it does NOT own → sibling
## <body: triage/workflow → decision table → rules → code>
## Rationale
## Deviation considerations
## Common Mistakes
## Review Checklist
## References        ← only if it has references/
## Related skills

Structure aids (use where they fit — not universal)

• Lead with a triage/workflow ("Step 1 capture context → 2 smallest fix → 3 verify") for procedural skills. Skip it for pure reference/glossary skills — don't manufacture a procedure.
• Front-load a decision table (situation→fix, or option/best-for/complexity) wherever the agent must choose a path before implementing.
• Add a ## Contents TOC only for genuinely long skills that a reader jumps around in — not by default; for a short linear skill it just costs tokens.

Two-tier depth (references/)

Keep SKILL.md scannable: decision logic, short paired WRONG/RIGHT snippets (one point each), quick tables. Move long migrations, full API references, and big samples into references/*.md and point to them from SKILL.md with a plain instruction ("for the full lock-vs-actor guide, read references/synchronization.md"). This is a documentation convention — the agent reads those files via normal file reads when your SKILL.md tells it to; there is no automatic lazy-load. It keeps the always-in-context cost low while letting depth exist.

Naming & granularity

• name is kebab-case; our consistency gate requires name to equal the directory (run mise run check) for clean cross-references and tooling. (Note: that's our rule — Claude Code itself derives the command from the directory and treats name as a label.)
• One surface area per skill. Where Apple ships a Kit, take the Kit name (widgetkit, storekit). For cross-cutting topics use a descriptive compound at the right altitude — swift-concurrency, not the too-broad swiftui nor the too-narrow swiftui-observable.

Reviewing a skill (CR)

When you CR a skill or a batch, apply the evidence-based, multi-lens doctrine (it caught real errors in this catalog):

• Diverse lenses, not one reviewer — for a batch, dispatch reviewers with distinct expertise (correctness, a11y, security, performance, skill-authoring). Different lenses catch what redundancy can't.
• Evidence for every falsifiable claim — a reviewer flagging "this API/version is wrong" cites the source (Apple docs / Swift Evolution / WCAG), not "looks off"; each lists "what I did NOT verify + confidence".
• Reviewers can be wrong → the Leader adjudicates — don't take the union on faith. Verify disputed falsifiable claims yourself before accepting or overruling (real cases: a reviewer "corrected" an iPhone-14-Pro size that was already right; another pushed a deprecated CLI form).

Common Mistakes

1. Vague one-line description — the agent can't route to it. Use the precision-router form with API names.
2. No negative boundary on a skill that can over-fire — it produces unwanted artifacts.
3. Description as summary, not router — it restates the body instead of naming trigger conditions.
4. No scope-boundary line — two adjacent framework skills both claim the same request.
5. Decisions buried in prose instead of a table/triage when the agent must choose a path.
6. Deep reference material inlined into SKILL.md, bloating always-in-context cost — move to references/.
7. Generic Common-Mistakes ("write good code") instead of concrete, anti-pattern-named items.
8. Project-specific workaround presented as general guidance (e.g. "avoid .task, our build has bug #361") — ships wrong advice to every consumer.
9. Stale/unverified API or version claim — cite the source; a wrong version gate emits needless #available guards or won't compile.

Review Checklist

• (General skill discipline checked against superpowers:writing-skills first.)
• name equals the directory; mise run check passes.
• description is router form: verb-anchored, embeds the triggering framework APIs, lists trigger scenarios; a negative boundary if it could over-fire.
• A scope-boundary line names what the skill does NOT own and routes to the sibling.
• Choices the agent must make are in a table/triage, not prose.
• Deep material is in references/*.md with an in-body pointer; SKILL.md stays scannable.
• Rationale + Deviation present; code uses current APIs with version gates marked inline.
• Common Mistakes are concrete and anti-pattern-named; no padding.
• No project-specific workaround dressed up as general guidance.
• Every falsifiable API/version claim spot-checked against an authoritative source (cite it).

Related skills

• superpowers:writing-skills — read first for the general discipline this skill deliberately does not repeat.
• claude-skill-plugin-packaging — packaging/distribution/discovery of the authored skill.
• subagent-review-cycles — the round structure the evidence-based CR plugs into.

Provenance

The structural patterns (router descriptions, bookend sections, two-tier references, naming) were distilled by studying high-quality public Swift/Apple skill collections — methodology only, no content copied — and combined with this catalog's own Rationale/Deviation convention and an evidence-based multi-reviewer CR doctrine. General skill-authoring doctrine is intentionally delegated to superpowers:writing-skills.