UX Motion Implementation

If you do not know these things, ask. Do not default to "add a nice animation." Default to understanding the context first.

Match what already exists. Before writing any animation, check the codebase for existing motion patterns: CSS custom properties for duration/easing, existing transition styles, animation libraries already installed. A new animation that uses different timing than everything else will feel wrong even if its values are technically correct. Consistency across the interface always beats a single perfect animation.

Motion Profiles by Product Type

Different products demand different motion energy. This is not subjective preference; it is UX strategy. The wrong motion personality erodes trust, creates friction, or makes the product feel juvenile.

For detailed motion recipes per product type with code examples, read references/context-patterns.md.

Core Principles

1. Timing: The Invisible Skill

Duration is the difference between "smooth" and "sluggish." The human brain has specific windows for processing visual change.

Scale duration to distance. An element moving 50px should animate faster than one moving 500px. An element changing size by 10% should animate faster than one expanding to full screen.

2. Easing: How Things Move

Linear motion feels robotic. Real objects accelerate and decelerate.

• ease-out (decelerate): Elements entering the screen. They arrive with energy and settle into place. This is your default for most UI motion.
• ease-in (accelerate): Elements leaving the screen. They start slow and speed away. Used less often.
• ease-in-out: Elements moving between positions on screen. Smooth start and stop.
• linear: Color changes, opacity fades, progress bars. Where constant rate feels natural.
• spring: When you need overshoot, bounce, or physics-based feel. Springs do not have fixed duration; they simulate stiffness, damping, and mass. This produces more natural motion than cubic bezier curves.

For the complete easing reference with cubic bezier values, spring parameters, and platform tokens, read references/easing-reference.md.

3. Choreography: Motion as Narrative

When multiple elements animate, their order and timing tell a story. Choreography is how you direct the user's attention.

Staggering: Delay child animations by 30-50ms each. Creates rhythm and directs the eye. Do not stagger more than 5-6 elements; after that, group them.

Sequencing: The most important element animates first. This establishes visual priority. Primary action leads, secondary content follows.

Parent-child: The container animates first, then children animate within it. Never animate children before their parent is in place.

Overlap: Sequences should overlap slightly. Do not wait for one step to fully complete before starting the next. A 10-20% overlap between steps creates fluid motion.

Total choreography budget: The entire stagger sequence should complete within 300-500ms. If your orchestrated animation takes longer than 700ms, users are waiting, not watching.

4. Motion as Communication

Every animation should serve one of these four functions:

If an animation does not fit one of these categories, question whether it should exist.

5. Consistency: Motion as a System

Individual animations do not exist in isolation. Every animated element is part of a larger motion language. If your modal enters at 250ms ease-out but your tooltip enters at 400ms ease-in-out, the interface feels disjointed even though both animations are individually fine.

Hierarchy of speed: Smaller, simpler elements should animate faster than larger, more complex ones. Tooltips < dropdowns < panels < modals < page transitions. This creates a natural rhythm where quick feedback is instant and context shifts take a beat.

Shared tokens: Define duration and easing values as design tokens (CSS custom properties or JS constants) and reuse them across all components. When every component draws from the same small set of timing values, the interface feels cohesive.

Exit vs. enter ratio: Exits should be 60-70% the duration of entrances. Users have already seen the element; they do not need as much time to process it leaving.

When Motion Feels Wrong

When a user says "this feels off," translate the subjective feeling into a specific parameter fix:

Component Motion Patterns

Performance

Animation performance is non-negotiable. Janky animation is worse than no animation.

GPU-accelerated properties (animate these)

• transform (translate, scale, rotate)
• opacity
• filter (blur, brightness)

These bypass the main thread and run on the GPU compositor. They produce smooth 60fps animation.

Layout-triggering properties (never animate these)

• width, height, top, left, right, bottom
• margin, padding, border-width
• font-size

Animating these forces the browser to recalculate layout for the entire page on every frame. This causes jank.

Rules

• Target 16.67ms per frame (60fps). On 120Hz displays, 8.33ms.
• Use will-change sparingly. Each promoted layer consumes GPU memory. Apply it only to elements that will actually animate, and remove it after.
• Prefer CSS transitions for simple state changes. Reach for JavaScript animation libraries only when you need orchestration, springs, or gesture-driven motion.
• Test on low-end devices. An animation that runs smoothly on a MacBook Pro might stutter on a budget Android phone.
• Measure with browser DevTools Performance tab. If frames are dropping, simplify.

Accessibility

Motion accessibility is not optional. It is a core requirement.

prefers-reduced-motion

Always provide a reduced-motion alternative. This is not "remove all animation." It means replacing motion with instant state changes or simple crossfades.

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

Better approach: instead of killing all animation globally, provide thoughtful alternatives per component. A slide-in panel becomes an instant appear. A staggered list loads all at once. A page transition becomes a crossfade.

Vestibular considerations

• 35% of US adults over 40 have experienced vestibular dysfunction
• Parallax scrolling, zoom animations, and spinning are the most problematic triggers
• Large-scale movement across the viewport causes more issues than contained, small-scale motion
• Auto-playing animations are worse than user-triggered ones

WCAG compliance

• 2.3.1 (A): No content flashes more than 3 times per second
• 2.3.3 (AAA): Users can disable motion from interactions unless it is essential to functionality
• Provide a motion toggle in your app settings when possible

Choosing the Right Tool

For implementation code patterns with each tool, read references/implementation-patterns.md.

Quality Check

Before delivering any animation code, verify:

Function

• Does every animation communicate something (feedback, spatial, state, attention)?
• Is the duration appropriate for the element size and travel distance?
• Does the easing match the direction (ease-out for enter, ease-in for exit)?

Performance

• Are you only animating transform, opacity, or filter?
• Did you test on a low-end device or throttled CPU?
• Is will-change used only where needed and cleaned up after?

Accessibility

• Does the animation respect prefers-reduced-motion?
• Is there a meaningful reduced-motion alternative (not just "no animation")?
• Does any content flash more than 3 times per second?

Context

• Does the motion personality match the product type?
• Would this animation annoy a user on their 100th visit?
• Is the animation interruptible? Can the user act before it completes?

Never

• Never animate width, height, top, left, margin, or padding. Use transform instead.
• Never block user interaction while an animation plays. All animations should be interruptible.
• Never add motion without a prefers-reduced-motion fallback.
• Never use bounce or spring easing in products where the context calls for restraint and trust. Match motion energy to the product's personality. When in doubt, err on the side of less.
• Never let a stagger sequence exceed 700ms total. After that, users are waiting.
• Never auto-play large-scale animations. User-triggered motion only, unless it is a loading indicator.
• Never animate more than 2-3 properties simultaneously on the same element. Each additional property increases the chance of jank.
• Never use animation duration as a way to "slow down" the user. If you need them to pause, use copy or a confirmation step, not a slow animation.
• Never apply the same generic animation to everything. A modal entrance and a tooltip entrance are different interactions with different needs.

Working With Other Skills

• ux-designer handles experience strategy, user flows, and interaction design. When the design reaches the point of implementing actual motion in code, this skill takes over.
• ui-designer handles visual styling, spacing, and component design. This skill handles how those components move and transition.
• ux-copywriter handles interface text. This skill may inform how text content appears (fade-in, typewriter effect) but the words themselves belong to ux-copywriter.