methodology / Performance / #32

Image optimization (WebP/AVIF)

#32 · Recommended · Web Quality · weighted · Performance · weight 1.3% · impl implemented · method v1.2.0

Web Quality factor

This factor is part of Web Quality — the weighted 0..100 score that sits above Web Standards. Its weight depends on what kind of site is being measured. Web Standards items take priority; this factor only enters the score once Web Standards passes.

Base weight: 0.7 applied to every site type unless overridden below
Why this weight: WebP/AVIF saves bytes on image-heavy sites.

Per-site-type overrides

Site type	Weight	Δ vs base
E-commerce	1.0	+0.3
News / Publisher	0.9	+0.2
Personal site	0.4	-0.3
Media / Streaming	1.0	+0.3

Site types not listed inherit the base weight.

Same factor, two depths.

What we measure

Modern image formats (WebP, AVIF) are 30-70% smaller than JPEG/PNG with no visible quality loss. Most browsers support them; serving JPEG to everyone wastes mobile bandwidth.

How to improve your score

Use a `<picture>` element with WebP/AVIF sources, or switch to a host/CDN that auto-converts (Cloudflare Polish, image CDN like Cloudinary).

Facts

Ticket

WEBQ-32

Scoring

Scoring formulas are versioned with the methodology. The current method (v1.2.0) maps raw measurements to pass, warn, fail. Factor weights determine how much each contributes to the composite — see the methodology index for the full table.

Cited by these standards

Standards in the Standards Library whose satisfiedBy requirement tree references this factor. Each link goes to the standard's full entry — methodology, scope, and the other factors it relies on.

Modern image formats (WebP / AVIF) Performance global WebP saves ~25–35% vs JPEG; AVIF saves ~50%. Either is supported by every browser that matters in 2026. Serving JPEG/PNG by default in 2026 is a self-inflicted byte tax.

Version history

Version	Change	Date
v1.2.0	Factor introduced. Status: live. Scoring impl: implemented.	2026-04-25

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