Interaction to Next Paint (INP) replaced First Input Delay (FID) as a Core Web Vital in March 2024. Unlike FID, which only measures the first interaction, INP considers all interactions throughout the page's lifecycle.
How INP works
INP observes all click, tap, and keyboard interactions and reports a value that represents the 75th percentile of interaction latencies. A low INP means your page consistently responds quickly to user inputs.
INP thresholds
- Good: 200 milliseconds or less
- Needs Improvement: Between 200 and 500 milliseconds
- Poor: More than 500 milliseconds
Why INP replaced FID
FID only measured the delay before processing the first interaction. INP provides a more complete picture by:
- Measuring all interactions, not just the first
- Including the time to process the event and paint the result
- Reporting a representative value, not a single measurement
Improving INP
- Optimize JavaScript execution time
- Reduce main thread work
- Break up long tasks
- Use
requestIdleCallbackfor non-critical work - Minimize forced synchronous layouts
Related Terms
Core Web Vitals
A set of three metrics defined by Google that measure the loading performance, interactivity, and visual stability of a web page.
First Input Delay (FID)
A deprecated metric (formerly a Core Web Vital) that measures the time from when a user first interacts with your page to when the browser can respond to that interaction.
JavaScript Execution Time
The time the browser spends parsing, compiling, and executing JavaScript code, which can block the main thread and delay interactivity.
Total Blocking Time (TBT)
A lab metric that measures the total amount of time the main thread was blocked long enough to prevent input responsiveness.