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First Input Delay

A Core Web Vital that measures the time from when a user first interacts with a page to the time when the browser is actually able to begin processing event handlers in response to that interaction.

AbbreviationFID
Categoryweb

Overview

FID measures the page's responsiveness during load. It captures the user's first impression of a site's interactivity and responsiveness. Note: Google is transitioning to Interaction to Next Paint (INP) as a more comprehensive responsiveness metric.

Why it Happens

FID usually occurs because the browser's main thread is busy doing something else (like parsing and executing a large JavaScript file), so it can't yet respond to the user.

Targets

  • Good: Under 100 milliseconds.
  • Needs Improvement: Between 100 and 300 milliseconds.
  • Poor: Over 300 milliseconds.

Related Terms

Core Web VitalsWeb Worker