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performanceVercel

Preload Fonts

MUST

MUST: Preload fonts for critical text to avoid flash & layout shift

Preload critical fonts to avoid flash and layout shift

Bad

Good

Why it matters

Font files take time to download, causing FOUT (flash of unstyled text) or FOIT (flash of invisible text). Preload critical fonts used for above-the-fold content using <link rel="preload"> to load them as early as possible.

References

Built by Gleb Stroganov, design engineer at Evil Martians.

The rules come from other people's skills and guidelines — Vercel, Rauno Freiberg, @Ibelick, impeccable, Emil Kowalski, Tailwind, RAMS — each one credited on the Sources page. The work here is extraction and wiring: every rule is pulled into one corpus, given a good and a bad example you can operate, a MUST/SHOULD/NEVER rule an agent can paste, and a link back to where it came from.