CDP Font.fontsUpdated event is not consistently emitted when fonts are preloaded

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Yonatan Sapojnik

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Jan 19, 2026, 12:52:40 PMJan 19
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Hi everyone,


I am monitoring font loading via the CDP, specifically the Font.fontsUpdated event.

Issue

When a page uses <link rel="preload"> to preload a font, the fontsUpdated event is not emitted consistently.

Observations

  • I use DevTools Protocol Monitor to listen for Font.fontsUpdated.

  • Network cache is disabled, so events should be emitted on every reload.

  • When the font is preloaded, the fontsUpdated event is sometimes missing.

  • When I remove the preload link, the event is emitted on every refresh.

  • When I inject the CSS via a <style> tag in <head>, the event is triggered more often, but still not consistently.

Expected Behavior

Font.fontsUpdated should be emitted consistently whenever a font is loaded and used, regardless of whether it was loaded via preload or regular CSS loading.

Actual Behavior

When fonts are preloaded, Font.fontsUpdated is emitted inconsistently or not at all.

Reproduction

Minimal repro attached below.

page.html
<!DOCTYPE html> <html> <head> <link rel="preload" href="./atelier_du_soleil.ttf" as="font" type="font/ttf" crossorigin="anonymous" /> <link rel="stylesheet" href="./my_css.css" /> </head> <body> <div class="preload-font"> This should be atelier du soleil! </div> </body> </html>

my_css.css
@font-face { font-family: atelier_du_soleil; src: url(./atelier_du_soleil.ttf) format("truetype"); } .preload-font { font-family: atelier_du_soleil; }

Notes

This behavior makes it difficult to reliably track font usage via CDP when preload is involved.


Thanks,
Yonatan

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