Check Last-Modified and If-Modified-Since

Checking Last-Modified and If-Modified-Since is an integral part of website promotion, required to understand whether the server's response headers are formed correctly.

Last-Modified is one of the server's response headers, which reports the date of the last change to the page, helping to assess how long ago the content was changed.

If-Modified-Since is a header sent to the server. It transmits a date to understand whether the page has changed since that date. If the content has changed, the server will return the page just as it would with a normal request, with a 200 response code. But if there have been no changes on the page, the server will return an empty page with the 304 Not Modified header.

If-Modified-Since is used by browsers to save traffic. For example, if the requested page is present in the browser's cache, it will create a request with the If-Modified-Since header. Next, if the response 304 Not Modified is returned, then the browser will display this page from its cache.

Properly configuring the server's response to the If-Modified-Since header also positively affects interaction with search engines, which save time on downloading an unchanged page and use it to process the next pages of the site.