CWV on EDS: Reference Material

Why EDS Sites Have Unique CWV Patterns

EDS achieves near-100 Lighthouse scores out of the box through strict architectural constraints. A vanilla EDS page with no customization typically scores at or near 100 on Performance. CWV issues are almost always caused by customizations that violate the built-in performance model: oversized images, blocks with heavy JavaScript, third-party scripts loaded in the wrong phase, or missing image dimensions. You are not fighting a slow framework. You are finding where customizations broke a fast baseline.

The Three CWV Metrics on EDS

LCP: Almost always an image issue. The 100KB budget means total eager-phase transfer must stay under 100KB. Check: hero image size, number of eager blocks, font preloading, third-party scripts in the eager phase.

CLS: Almost always an image dimensions or font swap issue. createOptimizedPicture() does not set width/height attributes on the images it generates. Late consent banners and font-display: swap without size-adjust are the other common sources.

INP: Almost always block JavaScript. Carousels, accordions, tabs, and mega-menus that do heavy DOM manipulation on interaction cause long tasks. Forced reflows (read layout then write DOM) are the most common code-level cause.

100KB Budget Grading Scale

The 100KB eager budget is the documented EDS threshold; the A-F banding below is this skill's own heuristic for triage, not an official Adobe grade. Use it to rank pages, not as a pass/fail standard.

CWV Threshold Reference

Projection Benchmarks

• Reducing an oversized source image's dimensions (e.g. 2000px → 1000px) saves 60-75% on the delivered derivative
• Content images are already delivered as WebP by the EDS picture pipeline, so format conversion is not a lever; only source dimensions and weight are
• Adding image dimensions eliminates image CLS entirely
• Font size-adjust reduces font CLS by 80-95%
• Debouncing and reflow batching reduce INP by 40-60%

Troubleshooting