There are many different factors that search engine crawlers may consider when crawling a website. Not every page will be indexed by search engines. The distance of a page from the root directory of a website may also be a factor in determining whether a page is crawled.
In November 2016, Google announced a major change to the way it crawls websites and began moving its index to mobile-first, meaning that the mobile version of a given website will become the starting point for Google to include its content in its index.
In May 2019, Google updated its crawler’s rendering engine to the latest version of Chromium (74 at the time of announcement). Google stated that they regularly update the Chromium rendering engine to the latest version.
In December 2019, Google began updating the User-Agent strings of its crawlers to reflect the latest Chrome versions used by its rendering services. The delay was to give webmasters time to update the code that responds to specific robot User-Agent strings. Google conducted an assessment and believes the impact will be minimal.
Prevent crawling
To avoid objectionable content in the search index, webmasters can instruct spiders not to crawl certain files or directories via a standard robots.txt file in the domain root directory. Additionally, pages can be explicitly excluded from the search engine's database using a robots-specific meta tag (usually <meta name="robots" content="noindex">). When a search engine visits a website, the robots.txt located in the root directory is the first file that is crawled. The robots.txt file is then phone number thailand parsed and instructs the robot which pages not to crawl. Since search engine crawlers may keep a cached copy of this file, it may sometimes crawl pages that the webmaster does not want to be crawled. Pages that are commonly blocked from crawling include login-specific pages (such as shopping carts) and user-specific content (such as search results from internal searches).