Animation Vocabulary

Animation Vocabulary

Turn a vague description of a motion or effect into the precise term, so the user knows what to ask for.

This cortex skill is vendored from emilkowalski/skills.

Quick Start

The user describes an effect loosely. You return the matching term(s) in this format:

**Stagger** — Animate several items one after another with a small delay between each, creating a cascade.

If several terms could fit, list the best match first, then 1–2 alternates with a one-line note on how they differ.

Instructions

1. Read for intent, not keywords. Users describe what they see or feel ("springy", "slides off", "draws itself in"), not the technical name. Map the sensation to the glossary below.
2. Quote the glossary verbatim. Its descriptions are authoritative — use them as-is, don't paraphrase.
3. Disambiguate close terms. When two compete (Clip-path vs Mask, Pop in vs Bounce, Shared element transition vs Layout animation), contrast them so the user can pick.
4. When nothing matches exactly, name the closest term and say plainly it's an approximation, or describe the effect in the glossary's vocabulary (e.g. "that's a stagger of scale-in entrances").
5. Stay within this glossary. If a term genuinely isn't here, say so rather than inventing one — though you may explain the concept using these words.
6. Keep it tight. A naming question wants a name, not an essay. Lead with the term; expand only if asked.

Examples

Example 1 — feel-based User: "What's it called when a popover seems to grow out of the button you clicked instead of from its middle?" Output:

**Origin-aware animation** — An element animates out of its trigger, like a popover growing from the button that opened it instead of from its own center which is the default in CSS.

Example 2 — disambiguation User: "The thing where one image turns into another image." Output:

**Morph** — One shape smoothly turns into another shape, e.g. Dynamic Island.

Close alternates:
- **Crossfade** — if they simply fade over each other in the same spot.
- **Shared element transition** — if an element travels and transforms from one position into another.

Example 3 — physics feel User: "That iOS scroll where it resists and snaps back when you pull too far." Output:

**Rubber-banding** — Resistance and snap-back when you drag past a boundary (the iOS overscroll feel).

Glossary

A curated snapshot mirroring the project's /vocabulary page; keep the two in sync when either changes.

Entrances & Exits — how elements appear and disappear

• Fade in / Fade out — Element appears or disappears by changing opacity.
• Slide in — Element enters by sliding in from off-screen (left, right, top, or bottom).
• Scale in — Element grows from smaller to full size as it appears, often paired with a fade.
• Pop in — Element appears with a slight overshoot, like it bounces into place.
• Reveal — Content is uncovered gradually, often by animating a clip-path or mask.
• Enter / Exit — The animation an element plays when it's added to or removed from the screen.

Sequencing & Timing — coordinating multiple elements or moments

• Keyframes — Defined points in an animation (0%, 50%, 100%) that the browser fills the gaps between.
• Interpolation / Tween — Generating all the in-between frames between a start and end value, so motion is continuous.
• Stagger — Animate several items one after another with a small delay between each, creating a cascade.
• Orchestration — Deliberately timing multiple animations so they feel like one coordinated motion.
• Delay — Time before an animation starts.
• Duration — How long an animation takes.
• Fill mode — Whether an element keeps its first or last frame's styles before the animation starts or after it ends (e.g. forwards).
• Stepped animation — An animation that is divided into discrete steps, like a countdown timer.

Movement & Transforms — changing an element's position, size, or angle

• Translate — Move an element along the X or Y axis.
• Scale — Make an element bigger or smaller.
• Rotate — Spin an element around a point.
• Skew — Slant an element along the X or Y axis, shearing it out of its rectangular shape.
• 3D tilt / Flip — Rotate in 3D space (rotateX / rotateY) to add depth.
• Perspective — How strong the 3D effect looks — a lower value exaggerates depth, like the viewer is closer.
• Transform origin — The anchor point a scale or rotation grows or spins from.
• Origin-aware animation — An element animates out of its trigger, like a popover growing from the button that opened it instead of from its own center which is the default in CSS.

Transitions Between States — connecting one state, view, or element to another

• Crossfade — One element fades out as another fades in, in the same spot.
• Continuity transition — A change that keeps the user oriented by visually connecting before and after. For example, making the same rectangle bigger and smaller.
• Morph — One shape smoothly turns into another shape, e.g. Dynamic Island.
• Shared element transition — An element travels and transforms from one position into another, like a thumbnail expanding into a card.
• Layout animation — When an element's size or position changes, it animates to the new spot instead of snapping.
• Accordion / Collapse — A section smoothly expands and collapses its height to show or hide content.
• Direction-aware transition — Content slides one way going forward and the opposite way going back, so navigation has a sense of direction.

Scroll — motion tied to scrolling or navigating between views

• Scroll reveal — Elements fade or slide into place as they enter the viewport.
• Scroll-driven animation — An animation whose progress is tied directly to scroll position.
• Parallax — Background and foreground move at different speeds while scrolling, creating depth.
• Page transition — An animation that plays when navigating from one page or route to another.
• View transition — The browser morphs between two states or pages, connecting shared elements.

Feedback & Interaction — responding to the user's actions

• Hover effect — Visual change when the cursor moves over an element.
• Press / Tap feedback — A subtle scale-down when an element is clicked, so it feels physical.
• Hold to confirm — A progress effect that fills up while the user holds a button.
• Drag — Moving an element by grabbing it, often with momentum when released.
• Drag to reorder — Dragging items in a list to rearrange them, while the others shift to make room.
• Swipe to dismiss — Dragging an element off-screen to close it, like a drawer or toast.
• Rubber-banding — Resistance and snap-back when you drag past a boundary (the iOS overscroll feel).
• Shake / Wiggle — A quick side-to-side jitter signaling an error or rejected input.
• Ripple — A circle expanding from the point of a tap, confirming the press.

Easing — how speed changes over an animation

• Easing — The rate at which an animation speeds up or slows down.
• Ease-out — Starts fast, ends slow. The default for most UI and anything responding to the user.
• Ease-in — Starts slow, ends fast. Usually avoided; can feel sluggish.
• Ease-in-out — Slow, fast, slow. Good for elements already on screen moving from A to B.
• Linear — Constant speed. Avoid for UI; reserve for spinners or marquees.
• Cubic-bezier — A custom easing curve you define for precise control.
• Asymmetric easing — A curve that accelerates and decelerates at different rates. Feels more alive than a symmetric one.

Spring Animations — physics-based motion as an alternative to fixed-duration easing

• Spring — Motion driven by physics (tension, mass, damping) rather than a set duration.
• Stiffness / Tension — How strongly the spring pulls toward its target. Higher feels snappier.
• Damping — How quickly a spring settles. Lower damping means more bounce and oscillation.
• Mass — How heavy the animated element feels. More mass makes it slower and more sluggish.
• Bounce — A spring that overshoots and settles, adding playfulness.
• Perceptual duration — How long a spring feels finished, even though it keeps micro-settling underneath.
• Momentum — Motion that carries velocity, especially after a drag or interruption.
• Velocity — How fast and in which direction an element is moving. A spring carries it into the next animation when interrupted, so a flicked element keeps its speed.
• Interruptible animation — An animation that can be smoothly redirected mid-flight instead of finishing first.

Looping & Ambient Motion — animations that run on their own

• Marquee — Text or content that scrolls continuously in a loop.
• Loop — An animation that repeats, a set number of times or infinitely.
• Alternate (yoyo) — A loop that plays forward then reverses each iteration, instead of jumping back to the start.
• Orbit — An element circling around another in a continuous path.
• Pulse — A gentle repeating scale or opacity change to draw attention.
• Float — A gentle, continuous up-and-down drift that makes a static element feel alive and weightless.
• Idle animation — Subtle motion that plays while an element is just sitting there, waiting to be interacted with.

Polish & Effects — the small touches that separate good from great

• Blur — A blur filter used to soften an element or mask tiny imperfections.
• Clip-path — Clipping an element to a shape, used for reveals, masks, and before/after sliders.
• Mask — Hiding or revealing parts of an element using a shape or gradient — like clip-path, but with soft, fadeable edges.
• Before / after slider — A draggable divider that wipes between two overlaid images to compare them.
• Line drawing — An SVG path that draws itself in, like an invisible pen tracing it.
• Text morph — Text that animates character by character when it changes, drawing attention to the new value.
• Skeleton / Shimmer — A placeholder with a moving sheen shown while content loads.
• Number ticker — Digits rolling or counting up to a value.
• Tabular numbers — Fixed-width digits so numbers don't shift around as they change. Essential for tickers, timers, and counters.
• Typewriter — Text appearing one character at a time, as if being typed.

Performance — what keeps motion smooth instead of stuttering

• Frame rate (FPS) — Frames drawn per second. 60fps is the baseline for smooth motion; 120fps on newer displays.
• Jank — Visible stutter when the browser drops frames because it can't keep up with the animation.
• Dropped frame — A frame the browser missed its deadline to draw, causing a tiny hitch in motion.
• Compositing — Letting the GPU move or fade an element on its own layer without redoing layout or paint.
• will-change — A CSS hint that an element is about to animate, so the browser can promote it to its own layer ahead of time.
• Layout thrashing — Animating properties like width, height, top, or left that force the browser to recalculate layout every frame, causing jank.

Principles to Know — concepts that guide when and how to animate

• Purposeful animation — Motion should serve a function — orient, give feedback, show relationships — not just decorate.
• Anticipation — A small wind-up in the opposite direction before a move, hinting at what's about to happen.
• Follow-through — Parts of an element keep moving and settle slightly after the main motion stops, adding weight.
• Squash & stretch — Deforming an element as it moves to convey weight, speed, and flexibility.
• Perceived performance — The right animation makes an interface feel faster, even when it isn't.
• Frequency of use — The more often a user sees an animation, the shorter and subtler it should be.
• Spatial consistency — Animating so an element keeps its identity and position across states, so users never lose track of where things went.
• Hardware acceleration — Animating transform and opacity lets the GPU keep motion smooth.
• Reduced motion — Respecting the user's prefers-reduced-motion setting by toning down or removing motion.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: tommylower
• Source: tommylower/cortex
• License: MIT

Install and usage instructions live in the source repository linked above.