transitions-dev

SKILL.md

Transitions.dev

Twenty-one portable CSS transitions, each namespaced under t-* selectors with semantic CSS custom properties. Drop-in: paste the snippet, wire the documented HTML hooks, done. No framework dependencies, no demo-specific markup, and every snippet ships a prefers-reduced-motion guard.

Quick reference

Transition
When to use
Reference

Card resize
Tween a container's width or height when its layout state changes.
01-card-resize.md

Number pop-in
Re-enter each digit with a blurred slide when a number updates.
02-number-pop-in.md

Notification badge
Slide a small badge onto a trigger and pop the dot.
03-notification-badge.md

Text states swap
Swap text in place with a blurred up-and-down transition.
04-text-states-swap.md

Menu dropdown
Open an origin-aware dropdown that grows from its trigger.
05-menu-dropdown.md

Modal open / close
Scale-up modal dialog with a softer scale-down on close.
06-modal.md

Panel reveal
Slide a panel into a region with a cross-blur.
07-panel-reveal.md

Page side-by-side
Slide between two side-by-side pages (list ↔ detail, step 1 ↔ step 2).
08-page-side-by-side.md

Icon swap
Cross-fade two icons in the same slot with blur and scale.
09-icon-swap.md

Success check
Compose fade + rotate + Y-bob + path stroke-draw to celebrate a completed action.
10-success-check.md

Avatar group hover
Distance-falloff lift on a row of items with a bouncy spring on return.
11-avatar-group-hover.md

Error state shake
Per-segment cubic-bezier shake with auto-reverting border + message.
12-error-state-shake.md

Input clear with dissolve
Fly-out + per-word streak when a text field is cleared.
13-input-clear-dissolve.md

Skeleton loader and reveal
Pulse a placeholder, then cross-fade + cross-blur to the loaded content.
14-skeleton-reveal.md

Shimmer text
Sweep a highlight band across muted text on a loop (pure CSS).
15-shimmer-text.md

Tabs sliding
Slide the active pill between tabs in a segmented control.
16-tabs-sliding.md

Tooltip open/close
Delayed fade+scale in, instant out (pure CSS).
17-tooltip.md

Texts reveal
Staggered blurred rise for stacked text lines, quiet fade out.
18-texts-reveal.md

Card hover tilt
Tilt a card in 3D toward the pointer with a cursor-tracked glare.
19-card-tilt.md

Plus to menu morph
Morph a circular trigger into the menu / panel it opens.
20-plus-menu-morph.md

Accordion expand
Grow / shrink a panel via grid-rows with a chevron flip.
21-accordion.md

Decision rules

When the user asks for a transition, match against the visible UI element first, then the verb:

Trigger + small dot floating on top → notification badge.

Trigger + surface that grows from it → dropdown (anchored, origin-aware) or modal (centered, no anchor).

Surface that slides into a region of the page → panel reveal.

Two screens, list ↔ detail or step 1 ↔ step 2 → page side-by-side.

Element changes width or height → card resize.

Element's text content changes in place → text states swap.

Two icons in the same slot → icon swap.

A number updates → number pop-in.

Confirmation / success / "done" moment (checkmark, payment processed, file uploaded) → success check.

Hovering an item in a horizontal stack (avatars, chips, segmented buttons, tag pills) → avatar group hover.

Form validation error / "this is wrong" feedback (invalid field, wrong PIN, duplicate name) → error state shake.

Clearing a text field (search box × button, filter reset) → input clear with dissolve.

Placeholder that loads then swaps to real content (list row, card, profile header) → skeleton loader and reveal.

In-progress / "thinking" text that should feel alive (loading label, streaming status) → shimmer text.

Small horizontal set of mutually-exclusive options with a moving highlight (view switcher, segmented control, filter tabs) → tabs sliding.

Hover/focus hint that appears over a trigger (icon tooltip, info bubble) → tooltip open / close.

Stacked headline + supporting line entering with rhythm (hero copy, empty state, onboarding step) → texts reveal.

Card / tile that should react in 3D to the pointer on hover (product card, cover art, membership card, with or without a light glare) → card hover tilt.

Circular trigger that becomes the surface it opens (+ FAB grows into a menu / panel, compose button expands) → plus → menu morph. If the surface is a separate popover that merely grows from the trigger, use menu dropdown instead.

Header with a collapsible body that grows / shrinks in height (settings group, FAQ, filter section, "show more", disclosure) → accordion expand.

No clear match → fall back to transitions reveal and let the user pick. Don't guess.

If two transitions could fit, prefer the lower-overhead one (card resize over panel reveal, dropdown over modal, success check over a full modal celebration) unless the design clearly calls for the heavier surface. The success check is animation-only — if you also need to swap from a spinner to the check, pair it with icon swap.

Commands

The skill exposes four namespaced verbs the agent should recognise in addition to direct transition requests. Every command starts with transitions so the invocation never collides with verbs from other skills installed in the same project.

transitions reveal — list every transition

Trigger phrases: transitions reveal, "reveal the transitions", "list all transitions", "what transitions are in this skill", "show the transitions catalog".

Behaviour: print the twenty-one transitions as a numbered plain-text list — name, one-line summary, and the matching reference filename. Reuse the rows in ## Quick reference above; do not invent new copy. No project access.

transitions review — audit the project for fit

Trigger phrases: transitions review, "review my project", "audit my animations", "where would transitions.dev help", "find places to use this skill".

Behaviour:

Search the workspace for indicators: transition: declarations, @keyframes, hardcoded ms / s durations in style files, components matching the decision-rule patterns (modals, dropdowns, badges, search inputs, skeletons, tabs, tooltips, …).

For each hit, match against the decision rules and pick the single best-fit transition.

Output a numbered list grouped by file:

path/to/Component.tsx:L42 — looks like a dropdown opening, suggest menu-dropdown (05-menu-dropdown.md).

Skip ad-hoc transitions that already use a t-* class.

Do not edit anything. End with: "Run transitions apply on any line to install the suggested transition."

transitions apply — install the best-fit transition

Trigger phrases: transitions apply, "apply a transition here", "add the right transition", "install transitions-dev here", "fix the animation on this element".

Behaviour:

Read context: the currently-open file, the element nearest the cursor, surrounding CSS / JSX. If the user named a transition explicitly (e.g. transitions apply menu-dropdown), use it.

Run the decision rules from ## Decision rules on that context and pick one transition. If two could fit, prefer the lower-overhead one (same tie-breaker the existing rules use).

Surface a one-line proposal: "I'd apply menu-dropdown here because the element opens from a trigger and is anchored. Confirm to install?".

On confirmation, follow the existing five-step procedure in ## Output format verbatim (root block, snippet, hooks, reduced-motion guard, JS orchestration if needed).

If the agent can't pick a single transition with confidence, fall back to transitions reveal and ask the user to choose.

transitions refine — replace ad-hoc motion with the motion tokens

Trigger phrases: transitions refine, "refine my transitions", "scan for ad-hoc transitions", "replace hardcoded durations with motion tokens", "tokenize my animations", "tune the durations / easing", "audit my custom keyframes", "make the timing consistent", "align to the motion tokens".

Behaviour:

Scan the whole project (not just dedicated stylesheets — also inline style= / CSS-in-JS, styled-components, <style> blocks, Tailwind arbitrary values like duration-[300ms]) for ad-hoc motion: transition / animation shorthands and longhands, custom @keyframes blocks, hardcoded durations (…ms / …s), easing (cubic-bezier(...) or keywords), translate distances (px), scale(...), and blur(...).

For each value, infer what the motion does (modal close, dropdown open, tooltip, badge appear, text reveal, page slide, shake, …) from the surrounding selectors / component plus the ## Decision rules. For a @keyframes block, read the animation that drives it and judge the keyframes' own duration/easing.

The key decision point is usage, not the raw number. Look the inferred usage up in ## Motion tokens and suggest the token whose documented usage matches — only when the usages line up. A 300ms modal close maps to --duration-quick because both are "modal close", even though the numbers differ. If a value's usage matches no token's usage, list it as no matching token usage and leave it untouched — never force a swap just because a number is close.

Output a numbered list grouped by file, showing only values that should change, each as path/to/Component.css:L42 — modal close: 300ms → var(--duration-quick) (150ms), ease → var(--ease-smooth-out). For keyframe-driven motion, suggest the token for the driving animation's duration/easing.

Do not edit anything. End with: "Confirm any line to apply the change, or run transitions apply to install a full transition instead."

Motion tokens

The shared motion scale behind the twenty-one transitions — the same tokens the transitions.dev Motion tokens tab exposes. They ship at the top of _root.css, so once it's imported you can reference any of them as var(--…) (e.g. transition: transform var(--duration-fast) var(--ease-smooth-out)).

transitions refine maps each existing value to a usage below, then suggests the token to reference. Match on usage, not on the raw number — a 300ms modal close still maps to --duration-quick (150ms).

Durations

Token
Value
Usage

--duration-stagger
40ms
per-item stagger offset

--duration-micro
80ms
tooltip/path delay, shake segment, large stagger

--duration-quick
150ms
modal/dropdown close, text swap, tooltip appear

--duration-fast
250ms
icon swap, dropdown/modal open, tabs sliding, page slide

--duration-medium
350ms
panel close, toast close

--duration-slow
400ms
panel open, skeleton content reveal, input clear

--duration-very-slow
500ms
emphasis moments, badge appear, text reveal, success check

Easings

Token
Value
Usage

--ease-smooth-out
cubic-bezier(0.22, 1, 0.36, 1)
modal/dropdown/panel open + close, page slide, resize, position change

--ease-in-out
ease-in-out
icon swap, text swap, text reveal, skeleton reveal

--ease-out
ease-out
tooltip open / close

--ease-linear
linear
shimmer, skeleton pulse, spinner

--ease-bounce
cubic-bezier(0.34, 1.36, 0.64, 1)
badge pop open

--ease-bounce-strong
cubic-bezier(0.34, 3.85, 0.64, 1)
bouncy hover-out (avatar return)

Distances

Token
Value
Usage

--distance-micro
4px
text swap

--distance-small
6px
error shake (small segment)

--distance-base
8px
badge diagonal reveal, page slide, error shake (large segment)

--distance-medium
12px
text reveal

--distance-large
30px
check badge appear

Scales

Token
Value
Usage

--scale-large
0.96
modal open / close

--scale-medium
0.97
dropdown open

--scale-small
0.98
tooltip open

--scale-tiny
0.99
dropdown close

Blur

Token
Value
Usage

--blur-small
2px
panel reveal, icon swap, text swap, skeleton reveal, number pop-in

--blur-medium
3px
page slide, text reveal

--blur-large
8px
success check open

Universal install

Copy _root.css into your project once and import it (or paste its :root block into your global stylesheet). It leads with the shared motion-token scale (--duration-*, --ease-*, --distance-*, --scale-*, --blur-* — see ## Motion tokens), followed by the semantic tunable variables for all twenty-one transitions. Every snippet reads from these names — --resize-*, --badge-*, --dropdown-*, --clear-*, --shimmer-*, --tabs-*, --tt-*, --stagger-*, --tilt-*, --morph-*, --acc-*, and the rest.

Each reference file also restates just the variables that snippet needs, so you can install a single transition without pulling the whole block. Don't duplicate the block — if _root.css is already imported, skip re-pasting any per-snippet :root.

The --pX-* source tokens used by the live demo at transitions.dev are intentionally not exported. Tunable values are renamed to semantic names so the user owns the design vocabulary. A few transitions (input clear, shimmer text, tabs, tooltip) carry color tokens that differ by theme — each reference file documents the html[data-theme="dark"] overrides.

Output format

When inserting a transition into the user's project:

Install the variables from _root.css into the user's global stylesheet, but only if they aren't already there — or just the per-snippet :root block from the reference file if installing a single transition. If the universal block is already imported, do not duplicate it.

Paste the chosen transition's CSS verbatim from the relevant reference file. Do not rewrite selectors, do not collapse the transition into shorthand, do not strip will-change. The snippets are tuned and tested.

Wire the documented HTML hooks — class names (.t-dropdown, .t-modal, .t-success-check, .t-avatar, .t-clear, .t-skel, .t-shimmer, .t-tabs, .t-tt, .t-stagger, .t-tilt, .t-morph, .t-acc, …) and state attributes (data-open, data-state, data-page, data-origin, aria-selected, aria-expanded, .is-open, .is-closing, .is-error, .is-shaking, .has-value, .is-clearing, .is-pulsing, .is-revealed, .is-shown, .is-hiding, .is-hover, .is-tilting).

Preserve the @media (prefers-reduced-motion: reduce) block. Every snippet ships one. Removing it makes the component fail accessibility audits.

For transitions that need JS (dropdown, modal, text swap, number pop-in, page slide, success check, avatar group hover, error state shake, input clear, skeleton reveal, tabs sliding, texts reveal, card hover tilt, plus → menu morph, accordion expand), copy the small orchestration snippet from the reference file and adapt the selectors to the user's DOM. Keep the timing reads (getComputedStyle(...)getPropertyValue("--…")) so durations stay in sync with the :root values. Shimmer text and tooltip are pure CSS — no JS needed.

Keep the diff small: only edit the files needed to introduce the transition. Don't rename the user's existing variables, don't reformat unrelated CSS, don't pull in a motion library.

Common mistakes to avoid

Stripping the close-state class cleanup on dropdown/modal — without the setTimeout that removes .is-closing, the next open jumps from the closing scale instead of the resting pre-open scale.

Forgetting the reflow in the text swap, number pop-in, success check replay, and error state shake — void el.offsetWidth (or offsetHeight) between class/attribute removal and re-addition is what guarantees the animation replays.

Animating a single container instead of the inner pieces — for the badge, animate the dot, not the trigger; for page slide, animate the page sections, not the container.

Replacing transition: … with transition: all — every snippet enumerates exact properties on purpose so unrelated style changes don't ride in for free.

Hardcoding the success check's stroke-dasharray — the snippet ships 20 as a placeholder. Replace it with path.getTotalLength() rounded up by 1 for your path, otherwise the stroke pre-reveals or over-draws.

Setting transition-timing-function in CSS for the avatar group hover — it has to be set inline in JS before the --shift / --scale-active writes so the bouncy ease-out only applies on mouseleave.

Mixing .is-error and .is-shaking into one class for the error state shake — keeping them orthogonal is what allows the shake to replay (remove → reflow → re-add) without flickering the whole error treatment.

Leaving the input clear glow on mix-blend-mode: multiply in dark mode — flip to screen, bump --glow-opacity to ~0.85, and paint white gradients in JS.

Forgetting to write the tabs pill's first position without a transition — on first paint and resize, set transform + width with transition: none (then reflow + restore) or the pill animates in from translateX(0) / width: 0.

Tracking the pointer on the tilting element itself for card hover tilt — bind pointermove to the flat outer .t-tilt wrapper, not .t-tilt-card, or the rotating edges slip under the cursor and the hover flickers.

Padding on the accordion grid track — put padding on .t-acc-panel-inner, never on .t-acc-panel; padding on the 0fr track leaves a residual height strip so the panel never fully closes.

Morphing the accordion chevron's d path — CSS d: path interpolation is Chromium-only, so it never animates on mobile Safari / Firefox. Flip the chevron vertically (transform: scaleY(-1)) instead — it passes through a flat line at the midpoint just like the path morph and works everywhere. Keep the path symmetric about its viewBox centre and add vector-effect: non-scaling-stroke so the stroke stays constant through the flip. This is what the snippet ships.

Reference files

01-card-resize.md — Card resize

02-number-pop-in.md — Number pop-in

03-notification-badge.md — Notification badge

04-text-states-swap.md — Text states swap

05-menu-dropdown.md — Menu dropdown

06-modal.md — Modal open / close

07-panel-reveal.md — Panel reveal

08-page-side-by-side.md — Page side-by-side

09-icon-swap.md — Icon swap

10-success-check.md — Success check

11-avatar-group-hover.md — Avatar group hover

12-error-state-shake.md — Error state shake

13-input-clear-dissolve.md — Input clear with dissolve

14-skeleton-reveal.md — Skeleton loader and reveal

15-shimmer-text.md — Shimmer text

16-tabs-sliding.md — Tabs sliding

17-tooltip.md — Tooltip open/close

18-texts-reveal.md — Texts reveal

19-card-tilt.md — Card hover tilt

20-plus-menu-morph.md — Plus to menu morph

21-accordion.md — Accordion expand

_root.css — the universal install block on its own, ready to import directly.