How Does PageSpeed Insights Assess Mobile Site Performance, and What Key Factors Should Be Optimized to Improve Scores?


PageSpeed Insights assesses mobile site performance using a mix of lab and field data to evaluate various aspects of a webpage’s loading and rendering. To improve your scores, emphasis should be placed on optimizing First Contentful Paint (FCP), Largest Contentful Paint (LCP), First Input Delay (FID), and other performance metrics by enhancing server response times, leveraging efficient asset delivery, and minimizing render-blocking resources. Below is a detailed guide to help you understand and improve your PageSpeed Insights score.

Overview of PageSpeed Insights

PageSpeed Insights (PSI) is a tool developed by Google to help website owners analyze and optimize the performance of their web pages. PSI provides separate reports for desktop and mobile devices, focusing on enhancing user experience through faster load times and smoother interactions.

Key Performance Metrics

First Contentful Paint (FCP)

FCP is the time from when the page starts loading to when any part of the page's content is rendered on the screen. To improve FCP, reduce render-blocking resources and optimize server response times.

Largest Contentful Paint (LCP)

LCP measures the time it takes for the largest content element (e.g. an image or text block) to become visible within the viewport. Optimize LCP by improving server response times, compressing assets, and deferring non-critical JavaScript and CSS.

First Input Delay (FID)

FID measures the time from when a user first interacts with a page to when the browser begins processing that interaction. Improve FID by minimizing JavaScript execution time, optimizing the main thread work, and using web workers to run scripts in the background.

Cumulative Layout Shift (CLS)

CLS quantifies how much visible content shifts in the viewport during the entire lifespan of the page. Reduce CLS by reserving space for images and ads, avoiding inserting content above existing content without warning, and applying consistent dimensions for media assets.

Optimizing Mobile Performance

Server Response Time Optimization

Improving server response times can significantly impact multiple performance metrics:

  • Utilize a Content Delivery Network (CDN) to reduce latency by serving content from locations closer to the user.
  • Implement server-side caching to quickly deliver pre-rendered pages or components, reducing Time to First Byte (TTFB).
  • Optimize database queries to minimize server load and response time.

Efficient Asset Delivery

Efficient delivery of assets, such as images, CSS, and JavaScript, is crucial for performance:

  • Use <link rel="preload"> to load critical resources early and improve page rendering times.
  • Compress images using modern formats like WebP and ensure text files are compressed using Gzip or Brotli [Enable Text Compression, 2021].
  • Use responsive images with <srcset> and <sizes> attributes to ensure images are appropriately sized for different devices.

Minimize Render-Blocking Resources

Minimize or eliminate resources that block the critical rendering path:

Optimize Web Fonts

The loading and rendering of web fonts can significantly impact performance:


Improving your PageSpeed Insights score requires a comprehensive approach, addressing various factors impacting load times and interactivity. By optimizing server response times, enhancing asset delivery, minimizing render-blocking resources, and optimizing web fonts, you can significantly improve your mobile site performance and user experience.