What Is React Profiler?

The React Profiler is a built-in performance analysis tool that helps you understand how your React application renders. It allows you to measure how often components render, why they render, and how long each render takes.

With this information, you can easily identify slow or unnecessary re-renders and optimize them to keep your application fast and responsive—especially as it grows in size and complexity.

Where Can You Use React Profiler?

React Profiler can be used in two main ways, depending on your needs.

1. React DevTools – Profiler Tab

This is the most common and beginner-friendly option.

Using the Profiler tab in React DevTools, you can:

Record user interactions (clicks, typing, navigation)
View flamegraphs showing component render order
See how long each component took to render
Understand why a component re-rendered

This visual approach is perfect for debugging real performance issues during development.

2. Profiler API

React also provides a programmatic API that lets you wrap components and capture render timings through a callback function.

This approach is useful when you want to:

Log performance data
Send metrics to analytics tools
Track performance in automated tests
Build custom performance dashboards

Key Metrics Explained

When profiling, you’ll see several important metrics. Here’s what they actually mean:

Metric	Description
actualDuration	Time (in ms) React spent rendering a component and its children
baseDuration	Estimated time to render the entire subtree from scratch
startTime	When React started rendering
commitTime	When React committed changes to the DOM
interactions	User actions (clicks, inputs) linked to renders

Understanding these metrics helps you decide where optimization is actually needed.

How to Use React Profiler (DevTools)

Using the Profiler via React DevTools is straightforward:

Open your React app in the browser
Open React DevTools
Go to the Profiler tab
Click Record
Interact with your app (click, type, navigate)
Stop recording

Once recording stops, you’ll see:

A flamegraph showing render order and duration
A ranked list of components by render time
Details explaining why each component rendered (state change, props change, context update, or parent render)

This makes it easy to spot performance bottlenecks and confirm whether renders were actually necessary.

Using the React Profiler API

Here’s a clean and corrected example of using the Profiler API:

import React, { Profiler, useState } from "react";

function onRenderCallback(
  id,
  phase,
  actualDuration,
  baseDuration,
  startTime,
  commitTime,
  interactions
) {
  console.log({
    id,
    phase,
    actualDuration,
    baseDuration,
    startTime,
    commitTime,
    interactions,
  });
}

function HeavyList({ items }) {
  return (
    <ul>
      {items.map((item) => (
        <li key={item}>{item}</li>
      ))}
    </ul>
  );
}

export default function App() {
  const [count, setCount] = useState(0);
  const items = Array.from({ length: 1000 }, (_, i) => `Item ${i}`);

  return (
    <>
      <button onClick={() => setCount((c) => c + 1)}>
        Re-render ({count})
      </button>

      <Profiler id="HeavyList" onRender={onRenderCallback}>
        <HeavyList items={items} />
      </Profiler>
    </>
  );
}

What’s Happening Here?

Every time HeavyList mounts or updates, onRenderCallback is triggered
React reports how long rendering took and why it happened
You can log this data, analyze it, or send it to monitoring tools

This approach is powerful for advanced performance tracking.

Best Practices for Profiling

To get accurate and useful results:

Profile production builds whenever possible (development mode is slower)
Focus first on components with long render times
Use React.memo, useCallback, and useMemo to prevent unnecessary re-renders
Avoid premature optimization—only optimize when performance impacts users

Common Use Cases

React Profiler is especially helpful for:

Identifying slow, deeply nested components
Debugging re-renders caused by changing props or state
Measuring performance before and after optimizations
Creating custom performance dashboards using Profiler API data

Conclusion

The React Profiler is an essential tool for building high-performance React applications. Whether you use the DevTools Profiler for visual debugging or the Profiler API for advanced tracking, it gives you deep insight into how your app renders.

By mastering the Profiler, you ensure your React apps stay fast, smooth, and scalable—even as features and complexity increase.

React Profiler Explained with Example