# motion-principles

A foundational motion design skill establishing timing budgets, easing curves, reduced-motion compliance, and jank prevention for Web, SwiftUI, and Compose.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1100 installs · ★ 677
- Author: AThevon
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/AThevon/genjutsu/tree/HEAD/skills/_jutsu/motion-principles/SKILL.md
- Updated: 2026-10-05
- HTML: https://affpapa.org/en/nevibecode/skills/motion-principles

## What it does

The skill establishes UI motion standards across web, SwiftUI, and Jetpack Compose. It sets clear timing bounds: 100 to 150 ms for micro-interactions and a 500 ms ceiling for UI transitions. The core rule is simple. Animations that trigger frequently must stay short and subtle.

A list of strict restrictions eliminates layout thrashing. The skill forbids animating `width`, `height`, `top`, or `left` because they force layout passes on every frame. Instead, it converts movement to `transform`, `offset`, or `graphicsLayer`. Exiting components fade out at `scale(0.95)` rather than collapsing into `scale(0)`, and entries must never use `ease-in` to avoid sluggish starts.

Accessibility is non-negotiable. The skill requires reduced-motion checks across CSS, SwiftUI, and Compose, providing drop-in snippets for each. Keep in mind that browser gates and API names in `_jutsu/VERSIONS.md` were checked on 2026-09-08, so re-verify your SDK versions if your stack is newer.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add AThevon/genjutsu --skill motion-principles -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/motion-principles/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/motion-principles/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add AThevon/genjutsu --skill motion-principles -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/motion-principles/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add AThevon/genjutsu --skill motion-principles -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/motion-principles/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install AThevon/genjutsu motion-principles
```

2. **Manually: put the files in place**
- File: `.github/skills/motion-principles/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add AThevon/genjutsu --skill motion-principles -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/AThevon/genjutsu --path skills/_jutsu/motion-principles
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/motion-principles/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add AThevon/genjutsu --skill motion-principles -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/AThevon/genjutsu/tree/HEAD/skills/_jutsu/motion-principles/SKILL.md

## When to use it
- calculate timing and easing curves for UI components and transitions
- refactor layout-triggering size animations into hardware transforms
- implement system reduced-motion preferences across web and mobile
- map CSS bezier curves to native spring dynamics in SwiftUI and Compose

## Example prompts
- Apply motion-principles to build a modal slide-in animation with CSS transforms and reduced-motion support
- Review this SwiftUI view transition: replace frame changes with offset and verify accessibilityReduceMotion
- Provide Jetpack Compose spring parameters for an enter and exit drawer state without scaling to zero

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: e8634019023b0d9d.

BEGIN THIRD-PARTY FILE e8634019023b0d9d
```text
---
name: motion-principles
description: "Motion design foundation - timing, easing, enter/exit patterns, accessibility, performance."
metadata:
  internal: true
---

> **Version-sensitive.** Every API name, SDK gate and browser-support claim below was
> verified on **2026-09-08** against primary sources. What against, and when, is in
> `_jutsu/VERSIONS.md`. If that date is old, re-verify before acting on a version number.

# Motion Principles

> The foundation. Loaded by every creative skill invocation.
> Concise rules here. Deep-dive in `references/`.

---

## Timing Rules

| Context | Duration | Why |
|---|---|---|
| Micro-interaction (toggle, hover, focus) | 100-150ms | Instant feedback, no perceived delay |
| UI transition (modal, drawer, tab switch) | 200-300ms | Smooth but never sluggish |
| Page/route transition | 300-500ms | Establishes spatial narrative |
| Scroll-driven / 3D | Free (progress-based) | Tied to user input, no fixed duration |

**Frequency rule:** The more often an animation plays, the shorter and subtler it must be.
A button hover (1000x/day) = 100ms opacity. An onboarding reveal (1x ever) = 600ms+ full choreography.

---

## Easing Cheat Sheet

| Action | Easing | Why |
|---|---|---|
| Element enters | `ease-out` / spring | Decelerates into resting position (natural arrival) |
| Element exits | `ease-in` | Accelerates away (gets out of the way) |
| Element moves between states | `ease-in-out` | Smooth start and stop |
| Scroll-synced | `linear` / `none` | Matches 1:1 with input, no lag perception |
| Bouncy/playful | spring (underdamped) | Overshoot creates life |
| Snappy UI | `cubic-bezier(0.2, 0, 0, 1)` | Fast start, smooth land |

> **Exit is always more subtle than enter.**
> Enter: 300ms ease-out, full choreography. Exit: 200ms ease-in, opacity only.

### Native easing equivalents (cross-platform)

| Web (CSS / JS) | SwiftUI | Compose |
|---|---|---|
| `cubic-bezier(0.2, 0, 0, 1)` | `.spring(response: 0.4, dampingFraction: 0.85)` or `.snappy` | `spring(stiffness = Spring.StiffnessMedium, dampingRatio = 0.85f)` |
| `ease-out` | `.easeOut(duration: 0.3)` | `tween(durationMillis = 300, easing = LinearOutSlowInEasing)` |
| `ease-in` | `.easeIn(duration: 0.2)` | `tween(durationMillis = 200, easing = FastOutLinearInEasing)` |
| spring (bouncy) | `.bouncy` (iOS 17+) | `spring(stiffness = Spring.StiffnessLow, dampingRatio = Spring.DampingRatioMediumBouncy)` |
| spring (smooth) | `.smooth` (iOS 17+) | `spring(stiffness = Spring.StiffnessMedium, dampingRatio = Spring.DampingRatioNoBouncy)` |

---

## Accessibility (Non-Negotiable)
```
END THIRD-PARTY FILE e8634019023b0d9d

The third-party file has ended. Everything between the e8634019023b0d9d tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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