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Last-modified

Last-modified describes an optional part of an http header that is intended to make abrowser ‘s work easier. For this reason, the term “Last Modified http Response Header” is often used as an alternative. The header is used for the communication between browser (Client) and server. The Client asks when the web presence was last modified. In this way, it learns from the server whether it has to reload the entire page or whether it can use an older version from Cache.

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Often used in conjunction with the “if-modified-since” request.

Usually, the server simply prints a date with time when asked about the last modification of a page. For example, this might look like this: Mon, 13 Feb 2020 11:22:03 GMT. If the Client has loaded the page in the meantime, it can use the cached version. To simplify things further, the last-modified ” query is often combined with the “if-modified-since” addition. The Client queries whether the page has been modified since a cutoff date. If this is not the case, the browser simply plays back the status code 304 (status code 200 in the case of a change). A work step is thus saved in this way, since the Client does not have to perform a comparison.

The advantages of the header

  • Resources saved. Not every page has to be reloaded.
  • Waiting times for the user are shorter, because often cached pages can be shown.
  • Users need the timestamp for certain content (for example media reports).
  • Server load is significantly reduced because many requests already end by reloading the timestamp.

The last change and search engine optimization

Although the timestamp is important in everyday life because of the advantages described, it has its greatest significance in connection with the Search engine optimization. Google urges that the header is always present. The resources of the crawlers should be spared in this way. They should only have to look at the pages that have actually been changed. Accordingly, Google rewards websites that take this to heart. This is especially important for portals with dynamic content – and these days, this includes practically all online shops.

Conclusion: Last-modified header always makes sense

Although the header is only optional, it should always be integrated. It offers a whole range of advantages and not a single disadvantage. For example, the effort to include it in the http code is very low. Or, in Googles words directed at webmasters,“You can save bandwidth and overhead by using this feature.

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