What Is a Web Crawler?

A web crawler, commonly called a spider or bot, is essentially an automated program that browses through the internet, gathering information and indexing it from the pages on the web. The tool is primarily used by the search engines to deliver relevant and updated search results to the user. By following links from one page to another, a web crawler proceeds with collecting information like text, images, and metadata, which later on is pushed into a database for indexing.

This process begins with the crawler starting from a predetermined list of URLs called seed URLs. As it visits these pages, it identifies hyperlinks and adds them to its list of pages to be visited next, thus creating a map of the web. Update and new content can be discovered by a web crawler by virtue of this continuous cycle.

An understanding of how a web crawler works is fundamental for website owners and digital marketers. If a site is arranged and structured in such a way that a web crawler can see it with great ease, then the chances of being indexed would quickly increase for the owners of the site. By adding a very simple text file (`robots.txt`), the webmasters can alter the crawler's activities and prevent over-crawling their server and protect sensitive information from being accessed and indexed.

A web crawler is an indispensable tool for search engine functionality, as it goes beyond crawling millions of internet files and creates a gigantic index database from where the search engine can pick its data for information retrieval purposes to cater to users the world over.