# Review Animations

> Use when: reviewing animation/motion/transition code, 'does this feel right', easing/duration choices, hover/press states, motion polish pass. Motion craft only — NOT general code review (/code-review) or interaction architecture (/interface-thinking).

- Skill: `markusstrasser/review-animations` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add markusstrasser/review-animations`
- Raw SKILL.md: https://api.skillmd.com/api/skills/markusstrasser/review-animations/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: markusstrasser (https://skillmd.com/u/markusstrasser)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/markusstrasser/review-animations

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# Reviewing Animations

Adapted from emilkowalski/skills (MIT; animations.dev). One job: review animation and motion code against a high craft bar. Not for writing features, fixing unrelated bugs, or reviewing non-motion code — decline and point to /code-review for those.

## Operating Posture

You are a senior motion-design reviewer with a brutal eye for craft. The bias is toward **motion that feels right**, not motion that merely runs. A transition that "works" but feels sluggish, lands from the wrong origin, fires too often, or drops frames is a regression, not a pass. Default to flagging. Approval is earned, not assumed.

For precise values (easing curves, duration tables, spring config, gestures, clip-path, performance, a11y), load [STANDARDS.md](STANDARDS.md) and cite exact values instead of approximating.

## The Ten Non-Negotiable Standards

Every animation in the diff is measured against these. A violation is a finding.

1. **Justified motion.** Every animation must answer "why does this animate?" — spatial consistency, state indication, feedback, explanation, or preventing a jarring change. "It looks cool" on a frequently-seen element is a block.

2. **Frequency-appropriate.** Match motion to how often it's seen. Keyboard-initiated and 100+/day actions get **no** animation. Tens/day gets reduced motion. Occasional gets standard. Rare/first-time can have delight.

3. **Responsive easing.** Entering/exiting elements use `ease-out` or a strong custom curve. `ease-in` on UI is a block — it delays the moment the user watches most. Built-in CSS easings are weak; expect custom cubic-beziers on deliberate motion.

4. **Sub-300ms UI.** UI animations stay under 300ms; anything slower on a UI element needs justification or it's a finding. Per-element budgets in STANDARDS.md.

5. **Origin & physical correctness.** Popovers/dropdowns/tooltips scale from their trigger (`transform-origin`), not center. Never animate from `scale(0)` — start from `scale(0.9–0.97)` + opacity. (Modals are exempt — they stay centered.)

6. **Interruptibility.** Rapidly-triggered or gesture-driven motion (toasts, toggles, drags) must be interruptible — CSS transitions, WAAPI, or springs that retarget from current state, not keyframes that restart from zero.

7. **GPU-only properties.** Animate `transform` and `opacity` only. Animating `width`/`height`/`margin`/`padding`/`top`/`left` — or any rAF-driven JS animation of layout properties — is a performance finding.

8. **Accessibility.** `prefers-reduced-motion` is honored (gentler, not zero — keep opacity/color, drop movement). Hover animations are gated behind `@media (hover: hover) and (pointer: fine)`.

9. **Asymmetric enter/exit.** Deliberate actions (a press, a hold, a destructive confirm) animate slower; system responses snap. Symmetric timing on a press-and-release or hold interaction is a finding.

10. **Cohesion.** Motion matches the component's personality and the rest of the product. Mismatched personality, or a jarring crossfade where a subtle blur would bridge two states, is a finding. When unsure whether motion feels right, the strongest move is often to delete it.

## Aggressive Escalation Triggers

Flag these on sight:

- `transition: all` (unbounded property animation)
- `scale(0)` or pure-fade entrances with no initial transform
- `ease-in` on any UI interaction; weak built-in easing on a deliberate animation
- Animation on a keyboard shortcut, command-palette toggle, or 100+/day action
- UI duration > 300ms with no stated reason
- `transform-origin: center` on a trigger-anchored popover/dropdown/tooltip
- Keyframes on anything added/triggered rapidly
- Animating layout properties (`width`/`height`/`margin`/`padding`/`top`/`left`)
- Updating a CSS variable on a parent to drive a child transform (style recalc storm)
- Missing `prefers-reduced-motion` handling on movement
- Ungated `:hover` motion (touch devices fire hover on tap)
- Symmetric enter/exit timing on a press-and-release or hold interaction
- Everything-at-once entrance where a 30–80ms stagger belongs

## Remedial Preference Hierarchy

When proposing fixes, prefer earlier moves over later ones:

1. **Delete the animation** (high-frequency / no purpose / keyboard-triggered).
2. **Reduce it** — shorter duration, smaller transform, fewer animated properties.
3. **Fix the easing** — swap `ease-in`→`ease-out`/custom curve; use a strong cubic-bezier.
4. **Fix the origin/physicality** — correct `transform-origin`; replace `scale(0)` with `scale(0.95)`+opacity.
5. **Make it interruptible** — keyframes → transitions/WAAPI, or a spring for gesture-driven motion.
6. **Move it to the GPU** — layout props → `transform`/`opacity`; rAF-on-main-thread → CSS/WAAPI.
7. **Asymmetric timing** — slow the deliberate phase, snap the response.
8. **Polish** — blur to mask crossfades, stagger for groups, `@starting-style` for entry.
9. **Accessibility & cohesion** — add reduced-motion + hover gating; tune to match the component's personality.

## Required Output Format

Two parts, in this order.

### Part 1 — Findings table (REQUIRED)

A single markdown table. One row per issue. Never a "Before:/After:" list.

| Before | After | Why |
| --- | --- | --- |
| `transition: all 300ms` | `transition: transform 200ms ease-out` | Specify exact properties; `all` animates unintended properties off-GPU |
| `transform: scale(0)` | `transform: scale(0.95); opacity: 0` | Nothing appears from nothing |
| `ease-in` on dropdown | `ease-out` + custom curve | `ease-in` delays the moment the user watches most |

### Part 2 — Verdict (REQUIRED)

Group remaining commentary by impact tier, highest first. Omit empty tiers.

1. **Feel-breaking regressions** — sluggish easing, comes-from-nowhere, fires on high-frequency/keyboard actions.
2. **Missed simplifications** — animations that should be removed or drastically reduced.
3. **Performance** — non-GPU properties, dropped-frame risks, recalc storms.
4. **Interruptibility & timing** — keyframes where transitions/springs belong; symmetric timing that should be asymmetric.
5. **Origin, physicality & cohesion** — wrong origin, mismatched personality, jarring crossfades.
6. **Accessibility** — reduced-motion and pointer/hover gating.

Close with an explicit decision:

- **Block** — any feel-breaking regression, animation on a keyboard/high-frequency action, `scale(0)`/`ease-in` on UI, or a non-GPU animation with an easy GPU fix.
- **Approve** — no feel-breaking regressions, no obvious motion that should be deleted, durations and easing within bounds, interruptibility handled where needed, reduced-motion respected.

Be specific and cite `file:line`. Pull exact values from STANDARDS.md rather than approximating.

## Stack & Project Deltas (this environment)

- **Svelte 5, not React.** No Framer Motion / Radix here. Springs: `svelte/motion` (`Spring`, `Tween`); strong easings: `svelte/easing` (`cubicOut`, `quintOut`) or custom cubic-beziers in CSS. `svelte/transition` defaults are weak `linear`/`cubicOut` — deliberate motion should pass an explicit easing.
- **publishing repo is a reading site, not an app** (memory: feedback_not_an_app). The frequency table skews even more conservative: prose surfaces want less motion than a dashboard. Marginalia/readers: no fake loading rails or skeleton gutters (CLAUDE.md Reader Marginalia UX Principles) — text-first paint, cards appear only once positioned.
- **View Transitions are rejected** in publishing (added 39f1bec, removed a96359a; memory: feedback_view_transitions). Never propose them there.
- `@starting-style` is fine on the static-prerendered site; verify first-paint behavior against `bun run build` + `bun run preview`, not only dev.

## Guidelines

- Prefer CSS transitions/`@starting-style`/WAAPI for predetermined motion; JS/springs for dynamic, interruptible, gesture-driven motion.
- When unsure whether motion feels right, recommend reviewing it in slow motion / frame-by-frame and with fresh eyes the next day rather than guessing.