PERFORMANCE · SEO GLOSSARY
WebP (SEO)
The WebP image format developed by Google — offering significantly smaller file sizes than JPEG and PNG at equivalent visual quality — which improves page loading performance (LCP in particular) and is supported by all modern browsers, making it the recommended image format for web images.
Definition
WebP is a modern image format developed by Google that provides both lossy and lossless compression with significantly better efficiency than JPEG (for photographs) and PNG (for graphics with transparency). WebP is the recommended image format for web content because it produces smaller files than JPEG or PNG at equivalent visual quality — typically 25–35% smaller than JPEG for photographic content. WebP SEO relevance: (1) **LCP improvement**: since the LCP element is most commonly an image, reducing the image file size directly reduces the time required to download and render the LCP element. Smaller LCP images produce better LCP scores. (2) **Total page weight**: a page with many WebP images instead of JPEG/PNG images loads less total data, improving time to interactive and reducing data cost for mobile users on limited data plans. (3) **Core Web Vitals**: better LCP from WebP images contributes to the page experience ranking signal. Browser support: WebP is supported by Chrome, Firefox, Safari (since iOS/macOS versions circa 2020), Edge, and Opera — essentially all modern browsers. Legacy IE (no longer in active use) did not support WebP. Implementation: serve WebP images directly when browser support is confirmed (e.g., based on HTTP Accept header), or use the HTML `<picture>` element with a WebP source and a JPEG/PNG fallback: `<picture><source srcset="image.webp" type="image/webp"><img src="image.jpg" alt="..."></picture>`. Most modern CMS and CDN platforms serve WebP automatically when the browser supports it. Google PageSpeed Insights and Lighthouse flag non-WebP images as an optimisation opportunity.
Why it matters for SEO
WebP adoption is one of the most straightforward Core Web Vitals improvements available. Switching from JPEG to WebP for page images reduces LCP time for any page where the LCP element is an image — which is the majority of web pages. The implementation effort is low (most modern image pipelines, CDNs, and CMS platforms can handle WebP conversion automatically), making the return on effort very high.
How DeepSEOAnalysis checks this
DeepSEOAnalysis checks image format usage on audited pages: identifying images served as JPEG or PNG that would benefit from WebP conversion, and checking whether the LCP image is served in WebP format. CrUX LCP field data provides the real-world performance impact of current image format choices. Pages with poor LCP and large non-WebP images have a clear optimisation path.
GLOSSARY
Related terms
performance
LCP Image
The image element identified by Chrome as the Largest Contentful Paint (LCP) candidate on a page — the largest visible image in the initial viewport that determines the LCP timing score, typically the hero image, product thumbnail, or featured photo at the top of the page.
Read definition →performance
AVIF (SEO)
The AVIF (AV1 Image File Format) image format — offering even better compression than WebP (typically 20–50% smaller at equivalent quality) — which improves LCP and page performance but has less complete browser support than WebP, typically requiring a fallback strategy using the `<picture>` element.
Read definition →performance
Image Compression (SEO)
The process of reducing image file sizes through lossy or lossless compression algorithms — directly impacting page load speed, LCP times, and Core Web Vitals — and the SEO implications of image compression choices for page performance and ranking.
Read definition →performance
Lazy Loading SEO
The SEO implications of lazy loading — deferring loading of images and other resources until they enter the viewport — which improves initial page load performance but can harm LCP if the main content image is lazy-loaded, and can prevent off-screen content from being indexed if text content is lazy-loaded.
Read definition →performance
Performance Budget
A predefined set of constraints on web page performance metrics — such as maximum JavaScript bundle size, maximum LCP time, or maximum total blocking time — used to prevent performance regression as a website evolves, by alerting or failing builds when the page\'s performance metrics would exceed the defined thresholds.
Read definition →See how your site scores on WebP (SEO).
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