First Input Delay (FID)

The First Input Delay (FID) metric measures how long it takes for a user interaction (clicking a link, opening a menu, etc) to begin being processed by the event handlers. Think of it as the lag between the interaction and the result of that interaction. If the webpage is loading lots of Javascript, then the main thread will be busy parsing and executing this code and won't have time to process events. Reducing Javascript execution time and minimizing work on the main thread can help improve this score.

The scores we use come from a Google Lighthouse report and represent the 28 day average score for the homepage as measured by real users using Chrome. Websites should aim for FID of less than 100ms. Anything over 300ms is considered to be poor.

For more information, please read the documentation on Web.dev.