Check library · Speed and Core Web Vitals
Image uses a legacy format
Why it matters
WebP and AVIF are typically 25 to 50 percent smaller at the same quality.
What to do about it
Convert to WebP or AVIF with a fallback.
The engine generates this fix itself using the optimise_image strategy. It arrives in your queue as a complete artefact, because an incomplete fix never reaches the queue, and once you approve it the change is pushed and the page re-fetched to confirm it is live.
How it is weighted
These are the values the scoring actually uses, not a description of them. Priority is derived from all three rather than chosen, which is why a high-impact, low-effort finding surfaces above a severe one that would take a quarter to fix.
- Severity
- low
- Impact
- 25% of the weight this category can carry
- Effort
- 30%, where 100% is a project rather than a change
- Confidence
- 80% that a hit is a real problem rather than a pattern we misread
- Area
- Speed and Core Web Vitals
Other checks in Speed and Core Web Vitals
highServer response is slowslow_responseneeds a decisionmediumPage weight is largeheavy_pageneeds a decisionmediumVery large JavaScript payloadexcessive_javascriptneeds a decisionmediumRender-blocking stylesheets and scriptsrender_blocking_resourcesneeds a decisionlowImage has no width and heightimage_no_dimensionsfix writtenlowBelow-the-fold images load eagerlyimage_no_lazy_loadingfix written
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