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What is a crawler?

A crawler (or web crawler) is an Internet bot that automatically scans information across the Web to create an index of data. These crawlers are operated by search engines like Google and Bing. In this way, relevant web page results can be presented after user searches.

  • Making information accessible on the vast Internet
  • Presenting relevant search results to users
  • Operating according to certain defined rules
  • Automated program searches WWW in a methodical way

How a crawler works

In principle, a crawler is like an online librarian who indexes web pages to update web information and evaluate the quality of page content. These “web spiders” crawl over the web like spiders, so to speak, and act as automatic indexers or web robots. This process is also known as web crawling. The best known crawler on the web is the Googlebot. The crawler searches many websites, for example, to check words on the page and to find out where the words are used elsewhere. Crawlers create a large index that contains all the results. Simply put, the index is a list of words and the webpages that refer to those words. A crawler usually starts its work by visiting a list of websites it has visited before. During the visits, it also searches for other related websites that are worth checking. This allows crawlers to detect new pages or URLs, update changes to existing pages, and so on. When web crawlers visit a particular page, they go through the entire content of the page and then transfer it to their database. Once the data is collected, the words on the page are added to a search engine index. You can think of the index as a huge database of words. However, crawlers do not stop completely once they have indexed web pages. They check from time to time if changes have been made to the web pages. If there is something new, the index created is updated as well. There are so many websites today, and so many newly created, updated pages every minute of every day, that you can imagine the huge amount of work these crawlers do. For this reason, search engines have established some guidelines for the content to be crawled, the order of crawling and the frequency of crawling, etc. For example, a web page that is updated regularly may be crawled more frequently than one that rarely makes changes. All of these rules are designed to help make this entire process more efficient. Every search engine has its own crawlers that can be used to update web page data. It has to be said that crawlers play an important role in the Internet age. Without web crawlers, it is extremely difficult to find the desired information in such an enormous ocean of information.

What are crawlers needed for?

They are mainly used to produce copies of all the web pages visited for later processing by search engines, which indexes the downloaded web pages to enable quick searches. In some cases, crawlers can also be used to automate maintenance tasks on a page, such as checking links or HTML code. Crawlers can also be used to collect certain types of information from websites, such as e-mail addresses (for spam). Web crawlers usually start their crawling process from the most popular websites. Their main purpose is to convey the essence of the individual page contents. The pages on the Internet are connected by hyperlinks, so crawlers can recognize these links and follow them to the next pages. The relentless web bots do not stop until they have found all the content and connected websites. They then send the recorded information to a search index stored on servers around the globe. The whole process resembles a real spiders web (hence the name) in which everything is interwoven. Among other things, a distinction is made between e-mail, news, images, social media and video crawling. Crawlers are an essential part of every major search engine used to index and recognize content. Many search engine companies have their bots, for example the Googlebot is operated by the giant Google. Apart from that, there are several types of crawl that are used to cover certain requirements. They are extremely important and beneficial to a business because they can make the business accessible to the whole world and attract new users and customers.

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