demo · v135

Tell the user: this is a cold start

The motivation in the spec: web apps suffer bimodal load times because the browser's first paint after launch is dominated by process bring-up — out of the app's control. Without a signal, performance budgets treat both starts the same and developers chase a phantom regression. The new PerformanceNavigationTiming.confidence hint lets the app branch on cold-vs-warm and either tell the user, or omit the slow path from p75 dashboards.

NavigationTiming.confidence: ?
nav start → first paint
—
ms
nav start → FCP
—
ms
confidence
—
browser hint

the code

const entry = performance.getEntriesByType("navigation")[0];
if (entry.confidence?.value === "low") {
  banner.textContent = "Loading the app for the first time today…";
}

see also