v133 · performance

CPU Threshold Explainer

Chrome 133 freezes background tabs on Energy Saver mode only when CPU usage exceeds a threshold and none of the exemption conditions apply. Toggle the conditions below to see whether your page would be frozen.

checking freeze event support… checking navigator.scheduling…

Freeze conditions (ALL must be true): Energy Saver active AND tab hidden >5 min AND CPU exceeds threshold AND none of the exemptions below apply.

Scenario explorer — known tab types

Custom exemption checker

Configure your page's properties

Configure options above

Toggle the checkboxes to compute whether your page would be frozen.

What to do in the freeze event

document.addEventListener('freeze', () => {
  // Synchronously save critical state — you have ~1s
  localStorage.setItem('draft', editor.getValue());
  localStorage.setItem('scrollPos', window.scrollY);
  // Don't start new async work — it won't finish
});

document.addEventListener('resume', () => {
  // Restore state if needed
  const pos = localStorage.getItem('scrollPos');
  if (pos) window.scrollTo(0, parseInt(pos));
});