The “specify a cache validator” message is another web page optimization suggestion you may come across during a website check. A cache validator is used in the response header to validate that caching is present within a page and to set and confirm the cache length. For example, when you visit a web page, the cache validator will help determine if the page request requires a fresh download or, if this is a page you have visited before, if files can be retrieved from cache. Obviously, if the request must go through the origin server, then the request is going to take longer. However, if the cache is still valid, then you can take advantage of the benefits of cached resources and better performance. You can check this for yourself by visiting a page.
Specify a Cache Validator
What is a Cache Validator?
How to Specify the Cache Validator
Lighthouse is an open-source tool that is used to run an audit against your web pages and provides scores and suggestions for improving page performance, accessibility, SEO, and more.
PageSpeed Insights is a tool created by Google that reports on the performance of a page on both mobile and desktop devices, and provides suggestions on how that page may be improved.