Google does not currently support the JPEG XL image format in Google Images or Google Discover, and advises site administrators to use an HTTP 503 status code for temporary website downtime during critical maintenance, according to company official John Mueller.
The guidance, communicated via social media, clarifies Google’s official stance on emerging image technologies and best practices for maintaining search engine optimization during server outages, particularly after a critical PHP vulnerability known as PHP2Shell.
Mueller, a search advocate at Google, confirmed that the next-generation JPEG XL format is not recognized by Google’s image indexing and discovery platforms, stating this on Bluesky, a social media platform.
Google’s official documentation lists BMP, GIF, JPEG, PNG, WebP, SVG, and AVIF as the supported image formats for the src attribute of the img tag on web pages.
JPEG XL is an open-source image format offering significant advantages over classic JPEG, including up to 50 percent better compression, lossless recompression capabilities, High Dynamic Range support, and fast software decoding.
For websites currently using JPEG XL, Google recommends providing a fallback in a widely supported format such as AVIF, WebP, or standard JPEG, which can be achieved using the <picture> HTML element, ensuring content remains accessible and discoverable by Google.
Separately, Mueller provided advice for website administrators addressing server-side vulnerabilities, specifically referencing the PHP2Shell exploit, advising that sites taken offline for patching should return an HTTP 503 (service temporarily unavailable) status code.
Returning a 503 code signals to Google that the site’s unavailability is temporary, which helps prevent de-indexing and negative search engine optimization impacts; Mueller emphasized that using 404 (not found) or 500 (internal server error) codes, or allowing repeated timeouts, could negatively affect a site’s search ranking and visibility.
Source: Abondance
