What is the Speed Index?
Speed Index (SI) is one of the many metrics tracked by the Performance Scan on both desktop and mobile. Each metric captures a different aspect of your application's performance.
The resulting SI is shown in milliseconds:
The SI metric measures how quickly content is visually displayed during page load.
PageSpeed makes screenshots during the page load and computes the visual progression between those screenshots. The SI score is based on the differences in those screenshots.
Known issues that have a large impact are:
- Minimize main thread work
- Ensure text remains visible during Webfont load