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First Input Delay (FID)

What it is: Measures the time from first interaction with your page to the time when their browser begins that interaction. In other words, when a user clicks a button on your page, how long does it take for the action to start happening.

Goal: FID should be 100 milliseconds or less. More than 300ms and Google will rate this “Poor.”

First Input Delay

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Improving FID

FID can be hard to measure manually because of how quickly it typically happens, but you can use Google’s Lighthouse performance tool’s “Total Blocking Time” as a proxy for it.

Improving FID will almost always require custom engineering work because this metric is dependent on the efficiency of your frontend code. When deciding how to fix a poor FID score, look to optimize your JavaScript code, especially that imported from third-party libraries. You can also try to use more non-blocking tasks and minimize the amount of data transferred to your frontend after a user action.

More detailed information and actionable insights can be found on the official FID Core Web Vitals page by Google. As mentioned, keep in mind that some of these actionable items might require help from your engineering team:

Copyright © 2022 Manuel Weiss and Karl Hughes. All rights reserved.