feat(core): opt-in image dimension (CLS) validation#143
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Adds checks.images.dimensions. Reusing the existing image detection, it flags CMS image fields that expose no usable width/height and emits CMS-IMG-DIMENSIONS (warning) - a common cause of layout shift (CLS), since the app cannot reserve space before the image loads. Understands the common provider dimension shapes (width/height, dimensions.*, media_details.*, file.details.image.*, and Sanity asset.metadata.dimensions.*). Off by default; adds an images report group for the new code in HTML and JUnit output.
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What
Adds
checks.images.dimensions. Reusing the existing per-provider image detection, it flags CMS image fields with no usable width/height and emitsCMS-IMG-DIMENSIONS(warning).Recognizes the common provider dimension shapes:
width/height,dimensions.{width,height}(Prismic),media_details.{width,height}(WordPress),file.details.image.{width,height}(Contentful), andasset.metadata.dimensions.{width,height}(Sanity).Why
Images without intrinsic dimensions are a top cause of layout shift (CLS), a Core Web Vital on the 2026 SEO checklist - the app can't reserve space before the image loads.
Off by default
checks.imagesstays a master toggle (falsedisables the alt check); the object form{ dimensions: true }opts into this. Off by default since some providers keep dimensions out of band.How verified
{ dimensions: true }flags a dimensionless image; width/height anddimensions.*shapes pass; zero width/height is flagged.pnpm verifygreen (219 tests).Refs improvements/37.