Game Feel (Juice)

Makes an app's meaningful moments land — through coordinated motion, haptics, and sound. Animation technique lives in design/animation-patterns; confetti/badge generation lives in generators/milestone-celebration. This skill is the discipline layer: which events deserve feedback, on which channels, and how to verify nothing important is silent.

When This Skill Activates

Use this skill when the user:

• Says the app feels flat, lifeless, or "lacks juice/polish/delight"
• Wants celebrations designed (winners, streaks, reveals, score changes)
• Asks to design or review haptics (vocabulary, Core Haptics, .sensoryFeedback)
• Asks about sound effects, buzzers, countdown ticks, or fanfares
• Wants a feedback audit — do the right events fire the right channels?
• Is building a party/group game where the phone is shared, passed, or watched at a distance

Core Principles

1. Channels have different reach — match the channel to the audience

Channel	Who perceives it
Haptics	Only the person holding the device
Screen motion	Whoever is looking at the screen
Audio	The whole room
Torch / flash	The whole room, even in noise

A single-user utility can lean on haptics. A shared-phone or room-facing app (party games, kitchen timers, presentations) must put its signature moments on a room-scale channel. The most common juice failure: all feedback is haptic, and the phone is lying on a table.

2. Feedback scales with rarity

Tick < action confirmed < success < round complete < winner. If the rarest event (winning) fires the same pattern as a routine one (round end), the app has no climax. Reserve the biggest pattern, the confetti burst, and the fanfare for the rarest event.

3. Escalation must agree across channels

If the timer's ring turns amber at 10s and red at 5s, the haptic tier and any audio tick must escalate at the same thresholds. Cross-channel disagreement reads as broken, not layered.

4. Single-owner rule

Exactly one code layer fires feedback for a given event. When an engine and a view-store both react to "music stopped", the user gets a double-buzz. Decide the owner (usually the layer closest to the state machine) and make the other layer silent.

5. Juice amplifies meaning — it never decorates

Every effect must be attached to an event the user cares about. Ambient/always-on effects (background particles, looping glows) are texture, not feedback — keep them static or slow, and never let them compete with event feedback.

6. Every channel needs an accessibility story

• Motion → gate large-scale motion on Reduce Motion, with a static equivalent
• Haptics → user-facing toggle (the system provides no global haptics setting for Core Haptics)
• Sound → mute toggle independent of system volume; a deliberate, documented silent-switch policy

Decision Tree

What do you need?
│
├─ Which events should have feedback, and on which channels?
│  └─ → feedback-audit.md (event×channel matrix + three-lens audit)
│
├─ Design or review haptics (vocabulary, service architecture, APIs)
│  └─ → haptic-design.md
│
├─ Add a sound-effect layer (assets, latency, AVAudioSession coexistence)
│  └─ → sound-design.md
│
├─ HOW to animate a celebration/transition you've already decided on
│  └─ → design/animation-patterns (springs, transitions, symbol effects)
│
├─ Generate confetti / badge / milestone UI code
│  └─ → generators/milestone-celebration
│
└─ Animated SF Symbols for feedback moments
   └─ → design/sf-symbols (preset vocabulary)

Review Checklist

When reviewing an app's game feel, verify:

• Signature moments hit ≥2 channels (e.g. winner = motion + haptic + sound)
• Room-facing events use a room-scale channel (audio, display-size motion, torch)
• Rarity gradient exists — the rarest event has visibly/audibly the biggest feedback
• No channel disagreement — escalation thresholds match across visual/haptic/audio
• Single owner per event — no double-fire from two layers
• Score/number changes animate (.contentTransition(.numericText())) — values never teleport
• State changes transition — no hard cuts between phases of a flow
• Reduce Motion parity — every gated effect has a static equivalent conveying the same information
• User controls exist — haptics toggle; mute toggle if there's an SFX layer
• Loading/waiting states have anticipation — determinate progress or a live effect, not a bare spinner at a climactic moment

Reference Files

File	Content
feedback-audit.md	Event×channel matrix method, three-lens audit (runnable subagent prompts), scoring rubric, output format
haptic-design.md	API decision table, semantic-vocabulary service architecture, pattern design rules, lifecycle, pitfalls
sound-design.md	Minimal SFX kit, asset formats and latency, AVAudioSession coexistence with music, silent-switch policy, pitfalls

Related Skills

• design/animation-patterns — the how of every motion technique
• design/sf-symbols — symbol effect vocabulary for feedback glyphs
• generators/milestone-celebration — production confetti/badge/celebration code
• ios/accessibility-audit — Reduce Motion and assistive-tech verification

References

• Human Interface Guidelines — Playing haptics
• Human Interface Guidelines — Playing audio
• Human Interface Guidelines — Motion
• Core Haptics