What is the difference between FID and INP?

FID (First Input Delay) measured only the delay before the browser could process the very first user interaction. INP (Interaction to Next Paint) measures the full duration — from interaction to visual feedback — for all interactions throughout the page session. INP is a more comprehensive measure of interactivity.

What is a good INP score?

Good: under 200ms. Needs Improvement: 200–500ms. Poor: over 500ms. Google replaced FID with INP in March 2024 because INP better represents the ongoing interactivity experience of the full page session.

Why is my INP poor only on mobile?

Mobile CPUs are significantly slower than desktop CPUs. The same JavaScript that executes in 50ms on a desktop may take 300ms on a mid-range mobile device. INP failures that only appear on mobile are almost always caused by JavaScript that is too expensive to run on slower CPUs.

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Check Your INP / FID Score (Interactivity Core Web Vital)

Interaction to Next Paint (INP) replaced First Input Delay (FID) as Google's interactivity Core Web Vital in March 2024. INP measures how responsive your page is to all user interactions — clicks, taps, and keyboard input. FixTools checks your INP score and identifies what is causing interactivity delays.

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INP and FID measurement

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Main thread blocking time analysis

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JavaScript execution bottleneck identification

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How to use this tool

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Enter your URL to measure INP/FID and identify JavaScript execution issues causing interactivity delays.

How It Works

Step-by-step guide to check your inp / fid score (interactivity core web vital):

1
Enter your URL
Paste the page URL to test for interactivity issues.
2
Review the INP score
Check the INP value. Good: under 200ms. Needs Improvement: 200–500ms. Poor: over 500ms.
3
Identify blocking JavaScript tasks
Review the Total Blocking Time (TBT) and any reported long tasks. Identify which scripts are consuming main thread time.
4
Reduce main thread blocking
Defer non-critical scripts, remove unnecessary third-party scripts, or use Web Workers to offload heavy computation. Re-test after each change.

Real-world examples

Common situations where this approach makes a real difference:

High cart abandonment investigation

An e-commerce site investigates high checkout abandonment and discovers INP of 480ms on the cart page — interactions feel sluggish. A tag manager loading 14 marketing scripts is identified as the cause. Reducing to 5 essential scripts drops INP to 180ms.

Single-page application audit

A React application fails INP due to expensive component re-renders triggered by user interactions. A developer uses the INP report to identify the specific interaction patterns causing delays and optimises the component state management.

Google Search Console INP alert

A site owner receives a "Poor INP" alert in Google Search Console for mobile users. Running the FixTools check identifies a heavy image filtering JavaScript function as the main blocking task. Offloading filtering to a Web Worker improves INP from 520ms to 95ms.

When to use this guide

Use this when your page feels "laggy" or unresponsive to user clicks and taps, or when INP is flagged as Poor in Google Search Console.

Pro tips

Get better results with these expert suggestions:

Long JavaScript tasks are the primary cause of poor INP

INP is determined by how long the browser takes to respond to user interactions. Long JavaScript tasks on the main thread block the browser from responding to clicks. Identifying and breaking up these tasks is the core INP optimisation.

Reduce third-party JavaScript

Tag managers, chat widgets, analytics scripts, and marketing pixels all execute JavaScript on the main thread. A single poorly-written third-party script can cause INP to fail. Audit third-party scripts and remove non-essential ones.

Defer non-critical JavaScript

Add defer or async to all script tags that do not need to execute at page load. This reduces main thread blocking during initial load and improves both INP and TBT (Total Blocking Time).