First Input Delay (FID)

FID, or First Input Delay, is a metric that measures the time it takes for a website or web app to become interactive, meaning that it is able to respond to user input. This is an important measure of the user experience, as a long first input delay can make a website or app feel unresponsive and slow. In order to improve FID, website developers can use techniques such as optimizing the loading of critical resources, using code splitting to reduce the amount of JavaScript that needs to be parsed and executed, and reducing the number of long-running tasks that block the main thread.