Borrowing it
Nothing to install: this file belongs to cardstack/boxel. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/cardstack/boxel/main/.claude/skills/motion-page-transition/SKILL.mdgit clone --depth 1 https://github.com/cardstack/boxelWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/cardstack/boxel/motion-page-transition)<a href="https://agentmods.dev/skills/cardstack/boxel/motion-page-transition"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/motion-page-transition/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/cardstack/boxel/motion-page-transition"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/motion-page-transition.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00100 | $0.00711 |
| Opus 5.5 | $0.00040 | $0.00284 |
| Sonnet 5.5 | $0.00020 | $0.00142 |
| Haiku 4.5 | $0.00010 | $0.00071 |
Grade A, and why
motion-page-transition scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 64 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Page transitions: animateView / viewTransition
Two exports, one platform API:
animateView(update, options?)— Motion's document-level builder: returns aViewTransitionBuilderwith.add(),.class(),.crop(),.group(),.layout(),.old(),.new(),.enter(),.exit(), auto names, spring-driven groups, queued interrupts. Theupdatecallback may be async (this wrapper runs it inside Ember's runloop for you).viewTransition(update, root?)— plainstartViewTransition, optionally scoped to an element so a study morphs inside its own box without snapshotting the rest of the page. Falls back to just applying the update when unsupported, and skips the transition entirely under prefers-reduced-motion — you don't handle that.animateViewdoes not skip under reduced motion; checkprefers-reduced-motionyourself if the morph should not run.
Tag the elements that should fly with view-transition-name /
view-transition-class in CSS, then style ::view-transition-old/new/group
pseudo-elements or drive them through the builder.
The Keynote vocabulary
Think in three casts: MOVES (elements tagged on both sides — they morph), LEAVES (only in the old page — fade out first), ARRIVES (only in the new — fade in last). Sequencing those fades around the morph is what makes it read as Magic Move instead of a crossfade soup.
When a view transition is the WRONG tool
startViewTransition snapshots the page into bitmaps and animates the
bitmaps. Anything alive — running animations, video, canvas — freezes for
the duration. The gallery's filter deliberately uses layout=true +
<LayoutGroup> instead so two dozen live demos keep running while their
cards fly (see the comment block in
packages/choreo-gallery/realm/shell/gallery-grid.gts).
Choose by content ownership: use layout for same-view geometry, Choreo route
crossings for live DOM continuity, and view transitions when snapshot behaviour
is intentional. A route change alone does not imply a snapshot.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 5d ago First seen · 64 lines · 100 tokens per session scan A 3e458594f382
motion-page-transition is a skill published in the GitHub repository cardstack/boxel (27 stars, last pushed today), licensed MIT. It adds 100 tokens to every session and 711 once invoked, about $0.0004 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-10-21.
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