Server response time is the time that elapses from the browser's request to the first part of the response being received. It is the foundation on which the entire speed of a website rests – if the server responds slowly, optimising images and scripts will only improve the result marginally. The most common causes are undersized or shared hosting, slow database queries with a large catalogue, a missing cache, a large number of extensions in the content management system, and the server's distance from visitors. The solution should be sought in this order: turn on caching, remove unnecessary extensions, optimise queries, and only then consider stronger hosting. Measure response time repeatedly and at different times, since it varies significantly under load, for example during campaigns. With content management systems, the biggest source of slowdown tends to be the number of active extensions, which are loaded on every request regardless of whether they are needed.
See also: CDN and content distribution, Core Web Vitals, Server Log Analysis.
