WebP

An image format that produces noticeably smaller files than JPEG or PNG at comparable quality.

Serve it through a picture element or content negotiation so older clients still receive a fallback.

Convert at build time rather than on request, and keep the original for future re-encoding.

A format change is the rare speed win that needs no design or content decision.

Typical savings of a quarter to a third of image weight show up directly in Core Web Vitals.