CSS Motion Review: test results

Verdicts

Date

2026-10-29

Strong · claude-sonnet-5-5 (Claude Code alias "sonnet")

Right on all 3 cases, read by hand. On a logo strip that loops for 36 seconds it gave exactly two lines, the loop with no pause control (named as the Level A failure) and the missing reduced-motion rule, and left out the opacity fade and the transform-only hover. On a hero with a hover zoom it named the reduced-motion rule that only changes a background colour and the accordion that animates its height, and left out the toast whose rule really switches it off. On a clean slideshow with a pause button it answered exactly No findings.

Weak · claude-haiku-5-5 (Claude Code alias "haiku")

Right on all 3 cases, read by hand. It gave the same two findings as Sonnet on the logo strip and on the hero, with the same safe look-alikes left out, and answered exactly No findings on the slideshow. Its lines were indented by four spaces on one case and separated by a blank line on another, which the checks accept; the content is correct.

Note

Light test: three cases (two planted, one clean), one run per model; no comparison without the skill. The three page sections were written by us; each planted one carries a safe look-alike (a short opacity fade, a transform-only hover, a reduced-motion rule that really switches a toast off), and neither planted case has a comment pointing at the defect. Facts come from the public MDN, W3C and web.dev pages named in the notes, read on 29 October 2026; there are no owner-measured facts.

What was not measured

• Models other than the two named above were not run.
• Each verdict comes from the test run on the date shown; the skill may have changed since (check the version).
• Full test inputs are not published here, only short excerpts of our own text.
• Results on your own texts, languages and domains can differ.