---
name: appllama-app-design-skill
description: Build native-feeling, benchmark-quality mobile app screens (Expo / React Native). Use when designing or implementing any mobile UI — screens, flows, onboarding, paywalls, tab bars, sheets, settings, empty states — or when polishing motion, navigation, typography, dark mode, or perceived performance. Enforces Apple HIG fidelity, semantic colors, native controls, anti-slop discipline, navigation semantics (push vs replace, modal vs sheet vs overlay, the one-way doors where back must not exist), purposeful Reanimated motion, a full-motion simulator-verified iteration loop, and a study-real-apps-first workflow (pairs with the Appllama MCP). Trigger on "build a screen", "make this screen better", "design the onboarding", "wire up this flow", "polish the UI", "make it feel native", or any mobile design/implementation task.
license: MIT
metadata:
  author: Appllama (appllama.io)
  version: 1.3.0
---

# Appllama App Design Skill

You are building screens that will sit on a phone next to the best-designed apps
in the world. The user will compare your output to those apps within seconds of
launching it. This skill defines the bar and the method for clearing it.

## The Prime Directive: study before you draw

Never design a screen from imagination when you can study how top apps solved
the same screen. Real, shipping, revenue-ranked apps encode thousands of hours
of design iteration and A/B testing. Your first move on any screen is research:

1. If the **Appllama MCP** is connected, pull real screens for the category and
   screen type you are building (see the `appllama-usage` skill for the exact
   research playbooks). Study 20–30 screens before writing a line of UI code.
2. Extract the **pattern, not the pixels**: layout skeleton, information
   hierarchy, control choices, spacing rhythm, where the primary CTA sits, what
   gets an illustration vs. plain text, how progress is communicated.
   Note: every Appllama image and video carries a small Appllama watermark in
   the top-left corner. It is provenance, not design — ignore it when reading
   a screen (it may sit over the status bar or a back button) and never
   reproduce it in anything you build.
3. Then design **your** screen: same proven skeleton, your product's voice.
   Copying a competitor's screen 1:1 is both lazy and legally risky; shipping a
   screen that ignores every convention users already know is worse.

## Platform baseline

Default stack assumptions (override only if the project already differs):

- **Expo + Expo Router**, React Native, TypeScript.
- `react-native-reanimated` for motion, `react-native-gesture-handler` for
  gestures, `@shopify/flash-list` (or FlashList v2) for any list that can grow.
- `expo-image` for images (and SF Symbols via `source="sf:name"` on iOS),
  `expo-video` / `expo-audio` (never the deprecated `expo-av`).
- `react-native-safe-area-context` for insets. Never hard-code notch numbers.
- `process.env.EXPO_OS` over `Platform.OS` for compile-time platform checks.

## Native fidelity laws

These are the details that separate "web page in a wrapper" from "native app".
Violating any of them is a finding, not a style preference.

1. **Semantic colors, both themes, day one.** Use system/semantic color tokens
   (e.g. `Color` from `expo-router` on iOS: `Color.ios.label`,
   `Color.ios.secondarySystemBackground`; Material dynamic colors on Android).
   Every screen must render correctly in light AND dark before it is "done".
   Never pass semantic color objects into Reanimated animated styles — resolve
   to strings first.
2. **Native controls over rebuilt ones.** Switch, Slider, SegmentedControl,
   context menus, date pickers: use the native control or a faithful wrapper.
   A rebuilt toggle that animates 50 ms differently than iOS's reads as fake
   instantly.
3. **SF Symbols / Material Symbols for iconography.** On iOS prefer SF Symbols
   (`expo-image` with `sf:` sources, or `expo-symbols`); they inherit weight,
   optical size, and Dynamic Type behavior. Do not mix three icon families on
   one screen.
4. **Typography is hierarchy.** Use the platform type ramp (Large Title / Title
   / Headline / Body / Footnote on iOS). One display size per screen. Tabular
   numerals (`fontVariant: ['tabular-nums']`) for anything that counts, times,
   or prices. `Text selectable` on data users may want to copy.
5. **Continuous corners.** `borderCurve: 'continuous'` on every rounded
   rectangle. Squircles are the single cheapest "feels iOS" win that exists.
6. **Shadows via CSS `boxShadow`**, not legacy `shadow*`/`elevation` props.
   Shadows are for elevation logic, not decoration — one elevation system per
   app.
7. **Spacing rhythm.** Pick a base unit (4 or 8) and never leave it. Prefer
   flexbox `gap` over margin stacking. ScrollView padding goes in
   `contentContainerStyle`, never on the ScrollView itself.
8. **Safe areas and the Dynamic Island are part of the design.** Screens must
   be verified with content scrolled under the island / status bar (does the
   blur/fade treatment hold?), with the home indicator (does the bottom CTA
   clear it?), and in landscape if supported.
9. **Navigation titles belong to the navigator.** Use the stack's native title
   (and large-title collapse behavior on iOS) rather than a hand-rolled header
   whenever possible.
10. **Haptics are punctuation.** Selection tick when a value passes a step,
    light impact when something snaps home, notification success/error for
    outcomes — on the same frame as the visual, one per user action, never
    the only feedback. Never on scroll, never in loops.
11. **Format numbers like a product, not a database**: 1.4M, 38k, $4.99. Trim
    trailing zeros. Localize dates.
12. **Root scroll behavior**: screens that can ever overflow wrap content in a
    ScrollView (first component in the route) with
    `contentInsetAdjustmentBehavior="automatic"`. Use `useWindowDimensions`,
    never `Dimensions.get()`.

## Navigation laws

Navigation is the part of a screen a screenshot can't show, and users feel
it in ten seconds. Every transition answers three questions: what is the
destination to here, must the user be able to come back, and what does back
(chevron, iOS edge swipe, Android hardware back) do afterwards.

1. **Push goes deeper, replace moves on.** `router.push` when the user will
   want to return here; `router.replace` / `<Redirect>` when coming back
   would land in a state the world has moved past; `router.dismissTo(href)`
   for "finish this flow and land on X". Back undoes *navigation*, never
   *events*.
2. **Presentation is meaning.** A self-contained task with steps →
   `presentation: 'modal'` with its own stack and its own Cancel/Done; a
   short interruption (picker, filters, item options) → `formSheet` with
   detents, drag-to-dismiss; immersive content → `fullScreenModal` with an
   explicit Close; something floating over a still-visible screen (confirm
   card, lightbox, coach mark) → `transparentModal` overlay; destructive
   confirms → action sheet; item actions → native context menu; share /
   web / photo picking → the system controller, never a rebuilt route. A
   sheet that grows a second step was a modal all along; if a link could
   open it, it is a route, not a `useState` sheet.
3. **One-way doors leave the stack.** Sign-in on a wall app, finished
   onboarding (Skip included), a purchase, a completed session: guard with
   `Stack.Protected` and land with `replace`, so back can never re-enter
   the old state — Android back from home exits the app, never shows
   Login; a paid paywall never re-opens. But keep the user's *place*:
   sign-in demanded by one action (save, follow, buy) is a modal over the
   screen that completes the action where it was tapped, and a paywall
   opened from a feature dismisses back onto the feature, unlocked — never
   `replace('/(tabs)')` from there.
4. **Back is blocked in exactly two cases** — an irreversible request in
   flight (seconds, with visible progress) and unsaved work in a modal
   (ask first), both via `usePreventRemove` on the modal's root screen.
   Transient in-screen state (selection mode, an expanded search, an open
   in-screen sheet) consumes the first back, then back leaves. Anything
   else that traps back — a funnel, a rating prompt — is a defect; the
   edge swipe works everywhere else.
5. **Tabs are peers.** No slide between tabs, each tab keeps its own stack,
   re-tapping the active tab pops to its root; full-attention screens
   (composer, player, checkout) live in the root stack *above* the tabs.
   Deep links land with a real stack underneath (`initialRouteName` /
   `withAnchor`); cold start lands by state, splash held until session
   state has resolved — never a Login flash before Home.
6. **Study the grammar, not just the pixels.** Walking a winning flow on
   Appllama, note what each step *is* — push, modal, sheet — and copy that
   consistency.

## Anti-slop laws

AI-built apps share a look, and users file it under "template" within seconds.
Each of these is a *default ban* — there is always an override when the brand
explicitly asks for the thing AND you can articulate why it fits this product.

1. **No AI-default styling.** Purple/indigo gradient CTAs with a glow,
   glassmorphism on every card, mesh-gradient heroes, confetti for minor
   events, sparkles in headings — that is the model's house style, not
   design. Your palette, materials, and layout come from the reference
   screens you studied, never from the priors you'd reach for unprompted.
2. **One accent, locked.** Pick one accent color and it is THE accent on
   every screen — no blue CTA on one screen and teal on the next, no new hue
   appearing in screen seven. Neutrals carry the app; the accent is spent
   where the money is (primary action, active state, progress).
3. **One grey family.** Warm greys or cool greys — never both in one app.
4. **Shape lock.** One corner-radius scale, stated as a rule ("actions are
   pills, cards 16, inputs 8") and never violated. Mixed radii without a
   stated rule read as assembled-from-parts.
5. **No emoji as iconography.** Icons are SF Symbols / Material Symbols
   (fidelity law 3). Emoji appear only when the product's voice is genuinely
   chat-native or playful — sparingly, in content, never in chrome.
6. **One label per intent.** "Get started", "Start now", and "Begin" are the
   same intent — pick one phrasing and use it everywhere it appears.
7. **Emphasis stays in the family.** Emphasize a word with weight or italic
   of the same typeface; injecting a serif word into a sans headline (or vice
   versa) for visual interest is amateur.
8. **Ship full state cycles, not the happy path.** Static-successful-state-
   only is the default failure mode: skeletons must match the final layout's
   shape, empty states are composed (and say how to fill them), errors are
   inline and specific.
9. **The slop pre-flight is mechanical.** Before any flow reaches the
   simulator pass, count: distinct accent hues (must be 1), distinct corner
   radii (all from the stated scale), emoji in UI chrome (0), gradients
   without a brand reason (0), duplicate labels for one intent (0). A failed
   count is a fix, not a judgment call.

## Motion laws

Motion is the highest-leverage polish surface and the easiest to overdo.
Decide in this order:

- **The frequency gate comes first.** Met 100+ times a day (tab switch,
  keyboard, scroll, back) → the platform default and nothing else; tens a
  day (press, row select) → near-imperceptible, under 150 ms; occasional
  (sheets, modals, toasts) → standard motion; delight only on rare,
  first-time moments. Tabs never slide; screen transitions stay native.
  Passing this gate with zero lines of code is a success — when unsure,
  the strongest move is to delete the animation.
- **Name the purpose in one word** — feedback, spatial continuity, state
  change, preventing a jarring cut, explanation, delight — or don't build
  it. Data the user is reading never moves for style.
- **If a finger was involved, it's a spring.** Start from the live value
  (capture it on grab), hand the release velocity into the spring, pick
  the target from projected momentum so a flick commits, rubber-band past
  boundaries, stay grabbable mid-flight. One vocabulary per app —
  `{ duration: 400, dampingRatio: 1 }` to settle, `{ 300, 0.8 }` for
  sheets — and bounce only when the gesture carried momentum.
- **Everything else is timing, under 300 ms, strong ease-out**
  (`Easing.bezier(0.23, 1, 0.32, 1)` — built-in curves are too weak; never
  ease-in on an entrance). Press feedback lands on press-*in*, 100–150 ms:
  scale 0.97 on buttons and cards, a background highlight (never scale) on
  list rows, opacity on bar buttons. Exits are faster than entrances and
  leave the way they came in; enter from `scale(0.95)` + fade, never
  `scale(0)`; menus grow from their trigger (centered modals exempt).
- **Gesture → animation never hops the JS thread.** Worklets + shared
  values (`.get()`/`.set()`; `scheduleOnRN` — Reanimated 4's `runOnJS` —
  only at gesture end), `transform`/`opacity` only, no `entering` on
  recycled list rows, never animate a header's height (translate inside a
  fixed clip), keyboard-tracking UI via `react-native-keyboard-controller`
  — never a keyboard listener plus a guessed duration.
- **Respect Reduce Motion**: your spatial motion collapses to cross-fades;
  native transitions stay the system's.
- The bar: 60 fps through the hero flow, measured on a **release build on
  the slowest device you support** — Expo Go and dev builds hide exactly
  the jank you're hunting
  ([references/performance.md](references/performance.md)). Watch the
  recording once for feel, once frame by frame, and again next day with
  fresh eyes.

## State architecture

Screens that feel great are screens whose state is boring:

- **Server state** in TanStack Query (or the project's equivalent): caching,
  retries, optimistic updates. Never `useEffect`+`fetch`.
- **Client state** in a small atomic store (Zustand/Jotai). Broad "app state"
  contexts cause the re-render cascades that make UIs feel heavy.
- **Ephemeral UI state** (open/closed, focus, scroll) stays local to the
  component.
- **Optimistic by default**: taps reflect instantly, reconcile in the
  background, roll back loudly on failure.
- Uncontrolled `TextInput`s for high-frequency typing surfaces; controlled
  inputs are a top-3 cause of typing jank.
- Persist tiny client state in MMKV, not AsyncStorage, when latency shows.

## Perceived performance

- Skeletons only for content whose shape you know; otherwise progressive
  reveal. Never a full-screen spinner for a partial update.
- FlashList for every list; give stable keys.
- Preload the next screen's data on press-in, not on navigation-complete.
- Images: right-size sources, `expo-image` with `recyclingKey` in lists,
  thumbhash/blurhash placeholders.
- Cold-start TTI and bundle discipline live in
  [references/performance.md](references/performance.md) — apply the
  measure → optimize → re-measure loop, never blind memoization.

## Image & illustration assets

When a screen calls for illustration, empty-state art, hero imagery, or icons
beyond the symbol set:

- Generate assets with the **best image model available to you** (e.g. an
  imagegen tool or the Higgsfield MCP/CLI if connected) at the **highest
  quality settings**, then downscale to @1x/@2x/@3x. Never upscale.
- One visual language per app: pick a style (gradient-mesh, flat-duotone,
  3D-clay, hand-drawn, mascot style) and generate ALL assets in that same style, same
  palette, same lighting. A mixed-style asset set reads as template slop.
- Prompt for **transparent or solid-flat backgrounds** matched to your surface
  color; composite artifacts (white halos, wrong-color mattes) are an
  automatic redo.
- Full asset pipeline and prompt patterns:
  [references/image-assets.md](references/image-assets.md).

## The simulator loop (non-negotiable)

A screen does not exist until you have seen it running. The loop:

1. Implement → launch in the iOS Simulator (or Android emulator).
2. Screenshot and **actually look**: alignment, optical centering, spacing
   rhythm, truncation with long content, dark mode, Dynamic Type at XL.
3. Run the **full-motion pass** below — screenshots prove layout; they prove
   nothing about motion.
4. Fix, relaunch, re-verify. Repeat until you cannot find a defect — then run
   the checklist in [references/simulator-loop.md](references/simulator-loop.md)
   once more.

Do not declare a screen finished from code review alone. Do not stop at "looks
fine" — stop at "cannot find a flaw at 100% zoom".

### The full-motion pass (mandatory, per flow)

Every flow is evaluated as **moving pictures in the simulator, never as
stills**. Screen-record the entire flow end to end
(`xcrun simctl io booted recordVideo flow.mov`), exercising ALL of it:

- every screen transition, push/pop, tab switch
- every back path — chevron, edge swipe, Android hardware back — and, after
  each one-way door (sign-in, onboarding done, purchase, finished session),
  an attempt to go back that must fail to re-enter the old state
- every modal and sheet: present, drag, dismiss — and cancel mid-drag
- the keyboard, both directions: appear (does the layout glide, is the
  focused input visible?) and dismiss (does anything jump-cut?)
- every user interaction: press states, gesture follow-through, interrupted
  gestures, rapid taps, scroll flings at the extremes

Watch the recording **twice**: once at full speed for feel, once scrubbing
frame by frame. You are hunting:

- dropped or stuttered frames — the bar is a sustained **60 fps** through
  every transition, measured, not vibed
- one-frame flashes: white/unstyled first paint, wrong-theme frames mid-
  transition, color pops where a surface briefly renders the wrong token
- layout jumps, double-render pops, springs that clip or overshoot into
  content, elements that reflow after appearing

The whole recording must play like one native piece — smooth end to end,
zero UX glitches. One glitchy frame means the flow is not done.

## Definition of done, per screen

- [ ] Studied 10+ real reference screens for this screen type (via Appllama
      MCP when available) and can name the pattern you adopted
- [ ] Navigation answered: what this screen *is* (push / modal / sheet /
      overlay / replace), what back does from it on iOS and Android, and —
      behind a one-way door — that back cannot re-enter the old state
- [ ] Light + dark mode verified in the simulator
- [ ] Safe areas / Dynamic Island / home indicator verified
- [ ] Long-content, empty, loading, and error states designed — not defaulted
- [ ] Motion: the full flow screen-recorded and scrubbed — entrances,
      presses, transitions, modals, keyboard — native feel, zero glitch or
      wrong-color frames; Reduce Motion respected; 60 fps measured on a
      release build on the slowest supported device
- [ ] Dynamic Type XL doesn't break layout; text is selectable where useful
- [ ] All tap targets ≥ 44pt; contrast passes in both themes
- [ ] Assets: single style family, crisp at @3x, no compositing halos
- [ ] List surfaces virtualized; no controlled-input jank; no re-render storms
      (profiled, not guessed)

## References

| File | Load when |
|---|---|
| [references/native-controls.md](references/native-controls.md) | Choosing/wiring iOS+Android native controls, menus, pickers, sheets |
| [references/motion.md](references/motion.md) | Any Reanimated work: gestures, transitions, springs, layout animations |
| [references/performance.md](references/performance.md) | Jank, slow TTI, big bundles, memory leaks, profiling method |
| [references/image-assets.md](references/image-assets.md) | Generating illustrations/icons/hero art with image models |
| [references/simulator-loop.md](references/simulator-loop.md) | Final verification checklist + device matrix |