PageSpeed

PageSpeed is a family of open-source software and tools developed by Google to improve the loading speed and perceived performance of web pages. It comprises PageSpeed Modules, PageSpeed Insights, and the PageSpeed Library. PageSpeed Modules implement on-the-fly optimization inside a web server, with versions such as mod_pagespeed for Apache and the pagespeed_nginx_module for Nginx. These modules rewrite and optimize HTML, CSS, JavaScript, and other resources as they are served to clients, based on a ruleset. PageSpeed Insights is a web-based analysis tool that examines a page and provides actionable suggestions to improve performance, drawing on data from Lighthouse and other sources. The PageSpeed Library is a C++ library that implements the optimization rules and can be embedded in other software.

How it works: The modules apply a collection of rules such as minifying and compressing resources, inlining or deferring CSS and JavaScript, optimizing images, caching aggressively, and reducing the number of HTTP requests. They can also rewrite URLs, enable compression (gzip or Brotli), and adjust resource ordering to improve critical-path rendering. Configuration is required to balance performance gains with compatibility and functionality.

Impact and limitations: When properly configured, PageSpeed modules can reduce page load times and improve perceived performance, but they may conflict with dynamic content or custom scripts and require careful testing. Some features may affect accessibility or behavior and may need disabling in certain environments. The hosted PageSpeed Service was discontinued in 2012; today, PageSpeed is typically deployed on a site's own server infrastructure as a reference implementation for web performance optimization.