Website indexing is the process by which search robots visit various websites and collect information from their pages. After that, this information is entered into the databases and processed, resulting in an index that is used to search. In the process of indexing, the robot regulates the number of documents requested at one time within the website's quota, which depends on many parameters. At the same time, for large websites, where the number of documents is several times greater than this quota, it is necessary to rationalize the indexing quota: it means, so that the robot downloads new information and changes from the previous website analysis. Last-Modified Title. This title shows the time the document was last modified. This information is undoubtedly necessary and useful, for example, in a date search, a document without this title will not be displayed. But it does not itself affect the indexing process. In fact, Last-Modified is needed to determine whether to load the document or not. For example, if, when accessing the website, you make a request: provide a document if it has changed since March 1, 2018, the document will be provided only if it has been changed. This saves time. If-Modified-Since Title. At the first request, the robot makes a request without any conditions. And when you repeat it, it already uses If-Modified-Since. It indicates the date of the previous indexing of the document. According to the protocol, in this case, there can be three response options: - If the date is incorrect, the response will coincide with the GET request - If the document is changed, from the specified date, then the response will also coincide with the GET request - If the document is not changed, then the server must give the answer 304 NOT MODIFIDED. Having received the third answer, the robot should not download the document, thereby saving the quota for new or changed documents. Errors with Last-Modified and If-Modified-Since Titles. Various errors can occur when using these titles. The server may not return the Last-Modified title or send it with incorrect data. You can try to fix errors on the website yourself or ask for help from companies specializing in the technical audit of the website. A technical audit allows you to analyze a website for more than 50 SEO errors, while not only fixing them, but also providing consultations to prevent these errors from appearing again. The Sonar.Network service provides not only services for finding errors and their structuring. The website is validated, a daily report is prepared and submitted electronically in the cloud. For a fixed monthly fee, you get 24/7 online support. The statistics of this organization show that more than 95% of clients eliminate errors on their websites in the first month, thanks to clear instructions.