VercatusImage formats and sizing
Images are the largest resource type by bytes on the median home page (2025 Web Almanac, July 2025 crawl). Lighthouse recommends AVIF or WebP over JPEG and PNG for better compression, flags an image whose file is at least 4 KiB larger than needed for its rendered size (accounting for device pixel ratio), and recommends srcset/sizes or an image CDN; web.dev warns never to lazy-load the LCP image.
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AGrade A: official documentation or a standard. A grade describes the provenance of the sources above; it is not a probability that a change will work. The effect basis says how the size of the effect is known: measured by a study, taken from an industry report, only documented without a size, or not quantified.
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