Former Core Web Vital measuring interactivity delay, now replaced by Interaction to Next Paint (INP) as of March 2024.
First Input Delay (FID) was a Core Web Vital metric that measured the time from when a user first interacted with your page to when the browser could actually respond to that interaction. It captured the delay users experienced when clicking buttons, tapping links, or performing other interactive actions while the main thread was busy processing JavaScript.
Google deprecated FID in March 2024, replacing it with Interaction to Next Paint (INP) as the official Core Web Vital for measuring interactivity. While FID only measured the delay to the first interaction, INP provides a more comprehensive view of page responsiveness throughout the entire user session.
Why It Matters for AI SEO
FID's legacy remains important because it established interactivity as a ranking factor and helped shape current page experience standards. Modern AI-powered SEO tools still reference FID when analyzing historical performance data, and understanding its principles helps optimize for INP, which uses similar concepts but with broader measurement scope. AI content generation and optimization tools often create JavaScript-heavy implementations that can impact interactivity metrics. When using AI tools to generate dynamic content, implement chatbots, or create interactive elements, the underlying principles that FID measured—main thread availability and response time—remain crucial for user experience and search rankings.
How It Works
FID measured the processing delay, not the complete interaction time. When a user clicked a button, FID tracked how long the browser took to start processing that click, not how long it took to complete the action. Good FID scores were under 100ms, needs improvement fell between 100-300ms, and poor scores exceeded 300ms. The metric only triggered on actual user interactions like clicks, taps, and key presses—not hover effects or scrolling. This made FID a field-only metric, meaning you couldn't measure it in lab environments like PageSpeed Insights. Instead, you needed real user data from tools like Google Search Console's Core Web Vitals report or Google Analytics. To improve FID, developers focused on reducing JavaScript execution time, splitting large tasks into smaller chunks, and using web workers for heavy computations. These same optimization strategies apply to INP and remain relevant for AI-powered sites with complex interactive elements.
Common Mistakes
Many practitioners assumed FID measured total interaction time, but it only captured the initial delay. This led to confusion when optimizing for responsiveness—fixing FID didn't necessarily make interactions feel faster if the visual feedback was slow. Additionally, some focused solely on lab testing tools that couldn't measure FID, missing the real-world performance issues that only appeared with actual user interactions and varying device capabilities.