CSS & Rendering · AuditJet Glossary

FOUT (Flash of Unstyled Text)

A web font loading behaviour where text is initially rendered in a fallback font before the custom font loads, causing a visible flash and potential layout shift.

FOUT occurs when font-display is set to 'swap' — the browser shows fallback font text immediately, then swaps to the custom font when it loads. While FOUT prevents invisible text (FOIT), the swap can cause Cumulative Layout Shift if the fallback and custom fonts have different metrics. Using font-display: optional or size-adjust on the fallback font can mitigate CLS from FOUT.

Related terms

CLS (Cumulative Layout Shift)

A measure of the largest burst of layout shift scores for every unexpected layout shift that occurs during the entire lifespan of a page.

Monitor FOUT continuously

AuditJet tracks Core Web Vitals on a schedule with revenue impact alerts.

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