First CPU Idle

May 20, 2023

First CPU Idle is a crucial aspect of web performance optimization that refers to the point in time when a page’s main thread becomes idle for the first time after initial page load. In other words, it marks the moment when the browser has finished loading and rendering all critical resources and can now respond to user interactions. It is also known as First Interactive, and it is a performance metric that measures when a web page becomes interactive, ensuring that the page is responsive and usable.

How First CPU Idle Works

When a user visits a website, their browser begins to download and render its resources, such as images, code files, and stylesheets. This process is known as page load. During this time, the browser’s main thread is busy executing various tasks, such as parsing HTML and CSS, executing JavaScript, and rendering the page. As a result, the browser may become unresponsive or sluggish, leading to a poor user experience.

First CPU Idle is determined by analyzing the main thread’s activity and identifying the point where it becomes idle for the first time. This metric is typically measured in milliseconds and is essential to web performance optimization as it indicates when a page is ready for user interaction.

Importance of First CPU Idle

First CPU Idle is a vital metric as it measures the moment when the page is ready to respond to user interactions, such as clicking buttons or scrolling. This metric is essential for a seamless user experience as it ensures that the page is responsive and usable.

In addition, First CPU Idle is critical for search engine optimization (SEO) as it is a key factor in Google’s PageSpeed Insights ranking algorithm. If a page takes too long to become interactive, it can negatively impact its ranking in search engine results pages (SERPs).

How to Improve First CPU Idle

Improving First CPU Idle involves optimizing the performance of a web page by reducing its load time and improving its rendering speed. Some of the best practices for improving First CPU Idle include:

Minimize Resource Size

One of the most effective ways to improve First CPU Idle is to minimize the size of resources such as images, code files, and stylesheets. Resource size can significantly impact page load time, and reducing it can lead to faster load times and improved performance.

Web developers can minimize resource size by:

  • Compressing images
  • Minifying code files
  • Removing unnecessary code
  • Using web fonts instead of embedding text as an image

Reduce JavaScript Execution Time

JavaScript is one of the most critical resources for a web page, but it can also be a significant cause of slow page load times. Minimizing the execution time of JavaScript can improve First CPU Idle and overall page performance.

Some of the ways to reduce JavaScript execution time include:

  • Using asynchronous loading for scripts
  • Lazy-loading non-critical scripts
  • Removing unused scripts
  • Optimizing JavaScript code

Defer Non-Critical Resources

Deferring non-critical resources such as third-party scripts or images can significantly improve First CPU Idle. By deferring these resources, they will load after the main content, allowing the page to become interactive faster.

Optimize Critical Rendering Path

Optimizing the critical rendering path is another effective way to improve First CPU Idle. The critical rendering path is the sequence of steps the browser takes to render a web page. By optimizing this path, web developers can improve page load time and reduce the time it takes for the page to become interactive.

Some of the ways to optimize the critical rendering path include:

  • Minimizing the number of critical resources
  • Inlining critical CSS
  • Using browser caching