demo · v139

FPS Visualizer

When the page is in a critical loading phase, the new blocking="full-frame-rate" hint tells the renderer to throttle animation frames so the loader gets CPU. Start a fake load and watch the on-screen animation's measured fps drop until the load finishes — then pop back up.

v139 ships blocking="full-frame-rate" under origin trial. This page simulates the behaviour by manually capping requestAnimationFrame while a fake load runs — so you can preview the user-visible effect anywhere.

load progress

animation stage (measured fps below)

—

fps (current)

frames rendered

idle

phase

the markup

<!-- The "expect" link blocks the render-blocking phase -->
<link rel="expect" href="#hero" blocking="full-frame-rate">

<!-- ...later in the body... -->
<img id="hero" src="/big.webp" fetchpriority="high">

<!--
  While #hero loads, the renderer drops to a lower frame rate to
  reserve CPU for parsing & resource decoding. Once #hero parses,
  full-rate animation resumes.
-->

the markup

see also