:not to be confused with offline reader. for the search engine of the same name, see webcrawler. a web crawler is an internet bot that systematically browses the world wide web, typically for the purpose of web indexing. a web crawler may also be called a web spider, an ant, an automatic indexer, or (in the foaf software context) a web scutter.see definition of scutter on foaf project's wiki web search engines and some other sites use web crawling or spidering software to update their web content or indexes of others sites' web content. web crawlers can copy all the pages they visit for later processing by a search engine that indexes the downloaded pages so that users can search them much more quickly. crawlers can validate hyperlinks and html code. they can also be used for web scraping (see also data-driven programming). == overview == a web crawler starts with a list of urls to visit, called the seeds. as the crawler visits these urls, it identifies all the hyperlinks in the page and adds them to the list of urls to visit, called the crawl frontier. urls from the frontier are recursively visited according to a set of policies. if the crawler is performing archiving of websites it copies and saves the information as it goes. such archives are usually stored such that they can be viewed, read and navigated as they were on the live web, but are preserved as âsnapshots'. the large volume implies that the crawler can only download a limited number of the web pages within a given time, so it needs to prioritize its downloads. the high rate of change implies that the pages might have already been updated or even deleted. the number of possible urls crawled being generated by server-side software has also made it difficult for web crawlers t
Internet_search_algorithms Search_engine_software Web_crawlers