#1167: WG New Spec: Scroll-Triggered Animations

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Opened Nov 10, 2025

Specification

https://drafts.csswg.org/css-animations-2/#timeline-triggers

Explainer

https://github.com/explainers-by-googlers/scroll-triggered-animations/blob/main/README.md

Links

The specification

Where and by whom is the work is being done?

  • GitHub repo: None
  • Primary contacts:
    • @DavMila, Google, CSSWG participant
    • @flackr, Google, CSSWG participant
    • @tabatkins, Google, CSSWG participant, spec editor
  • Organization/project driving the specification: Google
  • This work is being funded by: Google
  • Primary standards group developing this feature: CSSWG
  • Incubation and standards groups that have discussed the design:

Feedback so far

  • Active horizontal reviews: We filed csswg-draft issue #13010 to solicit feedback from the broader CSSWG on the overall spec text. <!-- Link to an issue like https://github.com/webmachinelearning/webnn/issues/239, https://github.com/WebAssembly/spec/issues/1804, or https://github.com/w3c/did/issues/885, which itself links to the other horizontal reviews. If you haven't started the rest of the horizontal reviews, please consider doing so. -->
  • Multi-stakeholder feedback:
  • Major unresolved issues with or opposition to this specification: None
  • Status/issue trackers for implementations: <!-- Include links to [Chrome Status](https://chromestatus.com/), [Mozilla's](https://bugzilla.mozilla.org/), [WebKit's Bugzilla](https://bugs.webkit.org/), and trackers for other implementations if those are known to you. -->

You should also know that...

There is also a Web Animations component to this proposal but only the CSS Animations spec is up to date. We plan to update the Web Animations spec after the CSSAnimations spec has been reviewed in #13010. We expect the web animations API to reflect the css animations API.

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Discussions

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Comment by @jyasskin Nov 19, 2025 (See Github)

We have a week before the Blink folks will approve this Intent to Ship: https://groups.google.com/a/chromium.org/g/blink-dev/c/TZLFLjzt4II/m/nzUrqB4CAwAJ

Discussed Dec 1, 2025 (See Github)

Matthew and Serena: not yet

Jeffrey: this was approved by blinkdev to ship last week. There is still time for the working group to suggest changes, and then for the folks to make changes.

Lola: can we get to it soon, or should we reassign?

Matthew: I'll look at it tomorrow.

Serena: I'll have time this week.

Discussed Dec 15, 2025 (See Github)

Matthew to post the comment.

Comment by @matatk Dec 17, 2025 (See Github)

Hi @DavMila, thanks for your review request.

We appreciate this is an increasingly used pattern, and it's important to help authors to get it right. On those lines, we have several concerns:

  • The robustness of this pattern on sites in general - e.g. when afforded by scripting - can be poor. For example: triggers firing the wrong number of times; things going wrong if the user scrolls back. Have you considered how these issues may be resolved through standardization?

  • Historically, all page content was loaded in and was available to ATs - it might just be off screen, but could be explored. If content is loaded dynamically in response to scrolling, this could exclude some users. (It doesn't seem like that's inherent here, but it seems like a pattern that may more prominently emerge following this.)

  • Scrolling and animation can cause huge cognitive issues (e.g. distracting, disorienting). We have prefers-reduced-motion but we're not sure how much consideration has been given to providing guidance for authors on how to ensure an equitable UX - especially in cases of complex animations revealing - or even themselves acting as - content.

  • Does this interact with/affect the focus in any way?

There seems to be justification for an 'accessibility considerations' section, assuming ways to address these concerns are known, or could be found. APA WG would be happy to help by reviewing any content you might create for such a section.

We look forward to hearing your thoughts on the above.