This translation has not been editorially reviewed yet. The German version is authoritative. Deutsche Fassung →
Checking Speed Index: how quickly the screen fills up
Speed Index describes how quickly the visible area fills with content overall. Unlike LCP or FCP, it doesn't name a single point in time — it assesses the whole course of rendering.
- This value is especially useful for pages that build up gradually: two pages can have the same LCP, but one feels empty the whole time while the other shows content from the start.
- Because it's calculated from a sequence of frames, it only exists in the lab — it isn't collected in real visitors' browsers.
