---
title: "INP Analyzer - Test Interaction to Next Paint · Unlighthouse"
canonical_url: "https://unlighthouse.dev/tools/inp-analyzer"
last_updated: "2026-06-30T08:47:50.096Z"
meta:
  description: "Free INP testing tool. Analyze your Interaction to Next Paint score, find long tasks blocking the main thread, and improve responsiveness."
  "og:description": "Free INP testing tool. Analyze your Interaction to Next Paint score, find long tasks blocking the main thread, and improve responsiveness."
  "og:title": "INP Analyzer - Test Interaction to Next Paint · Unlighthouse"
---

</h1>

```

Unlighthouse on GitHub

# **INP **Analyzer

Find what's blocking your main thread and slowing down interactions.

**INP Analysis**

Enter a URL to analyze INP

## **What is Interaction to Next Paint? **

INP measures how quickly your page responds to user interactions like clicks, taps, and keyboard input. It captures the **worst interaction latency** during a page visit, reporting when the browser finally paints a response. Google replaced FID with INP as a [~~Core Web Vital~~](https://web.dev/vitals/) in March 2024.

Since INP requires real user interactions, lab tools like Lighthouse use **Total Blocking Time (TBT)** as a proxy. TBT measures how long the main thread was blocked by long tasks during page load—a strong predictor of poor INP.

### **INP Timeline **

Click

Processing

**Paint **

Good INP**≤200ms**

## **Common Causes of Poor INP **

### **Long Tasks **

JavaScript executing for >50ms blocks the main thread. Break up work with `requestIdleCallback` or `scheduler.yield()`.

### **Third-Party Scripts **

Analytics, chat widgets, and ads often block the main thread. Load them async or use Partytown to run in a web worker.

### **Hydration **

Framework hydration can block interactions. Use progressive hydration, islands architecture, or server components.

### **Large DOM **

Too many DOM nodes slow down style calculations and layout. Keep nodes under 1,500 and virtualize long lists.

### **Layout Thrashing **

Reading and writing layout properties in a loop forces synchronous reflows. Batch DOM reads and writes.

### **Bundle Size **

Large JavaScript bundles take longer to parse and execute. Use code splitting, tree shaking, and lazy loading.

## **Frequently Asked Questions **

<details>

<summary>**01**### **What is Interaction to Next Paint (INP)?**

</summary>

Interaction to Next Paint (INP) is a Core Web Vital that measures responsiveness. It tracks the delay between user interactions (clicks, taps, key presses) and the visual feedback. A good INP score is 200 milliseconds or less, indicating a responsive experience.

</details>

<details>

<summary>**02**### **How is INP different from First Input Delay (FID)?**

</summary>

INP replaced FID as a Core Web Vital in March 2024. While FID only measured the first interaction, INP measures ALL interactions throughout the page lifecycle and reports the worst one. This makes INP a more comprehensive measure of real-world interactivity.

</details>

<details>

<summary>**03**### **What causes poor INP scores?**

</summary>

Poor INP is typically caused by: long JavaScript tasks blocking the main thread, heavy third-party scripts (analytics, ads, widgets), unoptimized event handlers, layout thrashing from DOM manipulation, and large JavaScript bundles that take time to parse and execute.

</details>

<details>

<summary>**04**### **How do I improve my INP score?**

</summary>

To improve INP: break long tasks into smaller chunks using yield patterns, defer non-critical JavaScript, use code splitting to reduce bundle size, optimize event handlers to avoid forced layouts, move heavy computation to web workers, and audit third-party scripts for performance impact.

</details>

<details>

<summary>**05**### **Why does lab data show TBT instead of INP?**

</summary>

Total Blocking Time (TBT) is used as a lab proxy for INP because true INP requires real user interactions. TBT measures time spent on long tasks (>50ms) during page load, which correlates with interactivity. Field data from real users provides actual INP measurements.

</details>

### **Related Tools **

[**LCP Finder **](https://unlighthouse.dev/tools/lcp-finder) [** Score Calculator **](https://unlighthouse.dev/tools/lighthouse-score-calculator) [** INP Optimization Guide **](https://unlighthouse.dev/learn-lighthouse/inp) [** INP Glossary **](https://unlighthouse.dev/glossary/inp)