What is a Web Crawler?

Have you ever wondered what a web crawler was and why it’s beneficial for your website. Web crawlers are programs that go by many names, including spiders, robots, and bots, and these descriptive names sum up what they do, which is crawl across the internet to index or catalog web pages.

The term crawler is used to describe one way that these programs might move from one site to the next or around a single site. When the program looks at a webpage and sees a link, it can follow that link to a new page. Some crawlers follow every link, while some crawlers only follow a link if it meets a certain criteria relative to the goal of the program. Crawlers are used to explore websites in a very basic computer friendly way. They are always used in tandem with other functionalities that make these programs powerful tools. With the proper understanding of how they work and what they can do, web crawlers can be a powerful tool to maintain and enhance your website.

What Do They Do?

Web crawlers are both a core component in how search engines work and as a tool for monitoring the health and performance of websites. Each web crawler or spider is used for a variation on the same task, namely gathering structured information from an unstructured source. A crawler is used to move a program from one page to another allowing another portion of the program to read parts of the website and record information about what it sees. That information can then be used for a million different things. 

You could pull the title for each page the crawler visits into a database. Or store the url for every image used on a given website. With a more advanced crawler, you could compile all the items in an html table and make a calculation about the row, if it meets certain criteria and store those calculated values. 

Some web crawlers are used to monitor competitor pricing. Some are used to gather performance data for a fan’s favorite fantasy sport league. We’ll focus on two usages of web crawlers that are important for web management. 

Crawlers and Search Engines

An important usage of web crawlers, for example, is Google’s crawling and indexing engine. Google runs a vast array of web crawlers for use on different types of websites that use a number of technologies for displaying information. It might use one crawler for sites that use a lot of Javascript rendered content and another for a site that uses mostly static html files.  

Google then adds the information it stores from a website to its index, which is its map of the internet. Google doesn’t predict the content on a website. It uses crawlers to explore the site and stores relevant information that users put into search queries.

Web crawlers are also used to monitor the health of a website. For instance, a crawler might store all the links on a site that link to another part of the same site. It can then use that list to check if the links on the list are working or if they are pointing to broken pages. A crawler might be used to check if the images on a site are correctly optimized, allowing a site to load quickly and smoothly. A good example of a tool like this would be Screaming Frog. This tool is used by webmasters all over the world to quickly and easily crawl websites and perform maintenance that would otherwise take hours or days. With a tool like Screaming Frog this can be accomplished in just ten or fifteen seconds.

If you are interested in learning more about Web Crawlers or other useful webmaster tools, send us a message or give us a call at (847) 297-1700.

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