Abstract: Due to the size of the web and its dynamic nature, building an efficient search mechanism is incredibly necessary. A huge range of web content is regularly being added each day, and information is continually changing. Search engines are used to extract valuable info from the web. Web crawlers are the principal part of search engine. It's a computer program or software that browses the World Wide Web in an exceedingly methodical, automatic manner or in an orderly fashion. It is an important methodology for collecting information on, and keeping up-to-date with the quickly increasing web. This Paper shortly reviews the ideas of web crawler, its design and its varied types with specification and working.

Keywords: Web crawler, crawler frontier, web repository, distiller, focused crawling.