A web crawler, also known as a spider or spiderbot, is an internet bot that systematically browses the World Wide Web and is typically operated by search engines for the purpose of web indexing. Web crawlers copy pages for processing by a search engine, which indexes the downloaded pages so that users can search more efficiently. They work by starting at a seed, or list of known URLs, reviewing and then categorizing the webpages. Before each page is reviewed, the web crawler looks at the webpages robots.txt file, which specifies the rules for bots that access the website. These rules define which pages can be crawled and the links that can be followed. Web crawlers can validate hyperlinks and HTML code, and they can also be used for web scraping and data-driven programming.
Web crawlers are important because they enable search engines to index data on web pages and return the most relevant results based on queries. Most popular search engines have their own web crawlers that use a specific algorithm to gather information about webpages. Examples of web crawlers used for search engine indexing include Amazonbot, Bingbot, and Googlebot.
Web crawlers are also used for web scraping, which involves extracting data from websites for use in other applications. Web scraping can be used for a variety of purposes, such as price monitoring, lead generation, and market research.
In summary, a web crawler is a computer program that systematically browses the World Wide Web for the purpose of web indexing and web scraping. They work by starting at a seed, or list of known URLs, and reviewing and categorizing webpages. Web crawlers are important for search engines to index data on web pages and return relevant results based on queries. They can also be used for web scraping to extract data from websites for use in other applications.
