Apple HIG Skill

Use the distilled HIG references in references/hig/ through routing-index.md. The source snapshot and verified release measurements are in README.md.

Loading Protocol

Release 2026-09-27; Apple source snapshot 2026-09-12. For help, installation, version or capability questions, read only this entry point and the relevant README section. Do not load the HIG corpus for setup help. Installing or upgrading this skill includes its /duo slash command. After the skill folder is in place, check whether the host already offers /duo. If it does not, copy commands/duo.md into the host's custom slash-command or custom prompt directory (user-level unless the user asks for one project), confirm /duo is available, and tell the user if a restart is needed. Work directly in the conversation and the user's project; do not create a browser intake form, onboarding site, dashboard, or browser setup step.

Ordinary guidance is the default. Only an explicit request to apply enforce mode activates its procedure. Read references/enforce.md first in that case and check reviewer, Python and observation capabilities before loading the design guidance. A leading /duo, Use apple-hig in Duo mode, or an explicit request to adapt an existing app for iPhone Duo starts Duo mode: read references/duo.md and follow its stages. Questions about the command and ordinary Duo design questions stay ordinary guidance. Duo mode works only in the app's native code; it never produces HTML, SVG, or web mockups. Use the available Python 3.10+ interpreter (python3 or python); do not assume the executable name. Ordinary guidance also works without Python.

When Python is available, use the standard-library routing helper to resolve steps 2–6: save only the exact user request to a UTF-8 text file in a temporary directory outside the user's project, then run <python> "<skill-root>/scripts/hig_route.py" --request-file "<request.txt>". Read every file in its files list in bounded sections, completing any truncated read before continuing. Do not concatenate the entire set into one tool output; the helper output is metadata, not the guidance itself. Do not add your own instructions to the request text or promote inferred topics to initial matches. If the user explicitly excludes a platform/device/topic, pass the excluded topic IDs with --exclude-topic (repeat for each topic, including platform aliases matched inside an excluded phrase); record the user's reason. Keep a platform that is also positively requested elsewhere. Do not exclude topics merely to reduce context. Exclusions apply to direct and related selections, never to the 16 foundations. Without Python, apply the same steps and explicit exclusions manually.

Step 1 — Parse Task Context

From the user's request, identify:

• Platform(s): ios / ipados / macos / tvos / visionos / watchos
• Device/form factor: iPhone Duo when named or matched by its tier-2 triggers
• Components or patterns mentioned (buttons, tab bars, sheets, etc.)
• Frameworks or SDKs referenced (HealthKit, SiriKit, ARKit, etc.)
• Task type: design / review / spec / audit / guidance
• Mode: ordinary guidance by default. Activate enforce mode only when the user explicitly asks to apply it; mentioning the mode or asking what it means does not activate it. Duo mode starts only as described above.

Step 2 — Load Tier 1 (every design or review task)

Read all 16 files listed in routing-index.md under ## tier-1:

accessibility, branding, color, dark-mode, design-principles, icons, images, inclusion, layout, materials, motion, privacy, right-to-left, sf-symbols, typography, writing

These apply universally. Load them before answering.

Step 3 — Load Platform File (Tier 2)

Read routing-index.md → ## tier-2 platform-map. For each detected platform, load its designing-for-[platform] file. Also match the tier-2 map's device/form-factor and API triggers using standalone word/phrase/API-symbol matching. A Duo match loads both designing-for-iphone-duo and designing-for-ios; Duo is an iOS form factor. If "game" or "gaming" is mentioned, also load designing-for-games.

Step 4 — Keyword Scan (Tier 3)

Read routing-index.md → ## tier-3 trigger-map. Normalize the user request to lowercase. Match trigger strings as standalone words, phrases, or API symbols; plural, hyphenated and bare-symbol forms count (tab bars, full-screen, keyboardType). Never match a trigger merely because it appears inside an unrelated word. For example, AR doesn't match "tab bar," and AI doesn't match "explain." Load every matching file. Load each file at most once.

Step 5 — Related Expansion

Freeze the initial selection set as the tier-2 and tier-3 files selected in steps 3–4. Read only that set's related: frontmatter. Load the listed files once. Do not expand related lists from those newly added files.

Bind each initial topic to the exact platform/device/trigger text matched in the user's request. An inferred component concept is not a literal trigger match. A topic reached through related: stays related even when it is useful; never promote it to initial and expand it again. If semantic relevance calls for an additional reference, load that specific file without related expansion.

Step 6 — Tier 4 On-Demand

Read routing-index.md → ## tier-4 trigger-map (on-demand). Use the same standalone word/phrase/API-symbol matching rule. Load a tier-4 file only on direct keyword match, or if named in the initial selection set's related: list. Never expand from foundations, newly related files, or directly matched tier-4 files. These are niche — avoid loading broadly.

Step 7 — Answer or enforce

For explicitly requested enforcement, carry out references/enforce.md using the loaded source guidance. Ordinary guidance never starts that procedure.

For an ordinary guidance answer, quote the short operative source clause verbatim with all qualifiers intact, then give only the needed application. A compact table works for multiple states. Keep the rule and application distinct; do not paraphrase the quotation into a stronger, broader, or narrower rule. Before sending, delete sentences that do not answer a requested part. Check the actor, starting state, action and resulting state; do not substitute a similar neighboring scenario. Mention an API as the implementation of a rule only when the loaded source supports that relationship.

Do not add unrequested adjacent rules or measurements merely because they are loaded. Preserve the source's full scope: do not invent narrower device/state limits when applying a rule, and include every requested state it covers.

Apply the guidance for the named platform, device, orientation, and state. An explicit scoped exception takes precedence over a broader rule within that scope; apply that exception only to its stated platform, device and state. Do not invent a reconciliation for unresolved source conflicts; identify the conflict. Apply all other compatible loaded content. If a topic isn't covered by loaded files, load the specific relevant reference before answering; keep unrelated expansion bounded.

Non-Negotiables

• Cite exact values. State pt sizes, pixel densities, margins, and

timing values as they appear in the distilled files. Preserve source ranges and approximation qualifiers; do not invent or round values.

• Distinguish platforms. When behavior differs across platforms,

state each platform's rule explicitly. Never flatten to "generally."

• Preserve recommendation strength. Keep must, prefer, consider, examples, conditions, and exceptions distinct when answering; do not turn an optional recommendation into a requirement.
• Preserve logical conditions. Keep conjunctions and alternatives intact. A consequence stated for A and B does not establish the same consequence for either alone; an A-or-B option does not require both. Check the claim in the answer as well as its supporting clause.
• No invention. Every Apple rule, measurement, and API recommendation must

trace to a loaded reference. Distinguish Apple guidance from your own design choices. If unsure, say so and name the source.

• Terse and direct. Keep ordinary guidance focused on the requested rule.

File Locations

• Distilled reference files: references/hig/[topic].md
• Routing index: routing-index.md
• Opt-in enforcement procedure: references/enforce.md
• Guided iPhone Duo redesign: references/duo.md, references/duo-checklist.md;

/duo slash command (install it with the skill): commands/duo.md

• Frontmatter schema: each distilled file contains topic, tier,

platforms, category, triggers, and related fields.