Web Crawler: Everything you need to know

When it comes to technical SEO, it can be difficult to understand how it all works. But it’s important to gain as much knowledge as we can to optimize our websites and reach larger audiences. One tool that plays a large role in search engine optimization is none other than the web crawler.

What is a Web Crawler?

A web crawler is an automated program or bot that systematically searches websites and indexes the content on them. Primarily used to index pages for search engines, web crawlers are also used for coupon and comparison shopping apps, and SEO and RSS aggregation, among other tasks. Web crawlers access sites via the internet and gather information about each page, including titles, images, keywords, and links within the page. This data is used by search engines to build an index of web pages, allowing the engine to return faster and more accurate search results for users. Web crawlers may also be used to scrape or pull content from websites, monitor changes on web pages, test websites, and mine them for data. Web crawlers are also known as web spiders since they crawl pages on the World Wide Web.

web crawler

Why is Web Crawling important?

Web crawling is important to businesses because it is key to search engine functionality. It lets search engines index information and know what sites and pages exist so they can refer to this information when it’s relevant to a query.


Web crawling is part of a successful SEO and search strategy, in part because it makes business websites and business information discoverable. Without an initial crawl, search engines cannot know if your site or website data exists. An internal crawl of your site also helps you manage your site data, keeping it updated and relevant so the right information is discoverable when queried, and so that you reach the right audiences.

User satisfaction

Using an enterprise web crawler is also key to your business website’s search functions. Because crawling indexes your site data (without the hassle), you can offer users a seamless search experience and are more likely to convert them into customers.

Automation and time-saving

A web crawler automates data retrieval and enables you to drive engagement to your website by crawling internally and externally. This way, you can focus on creating content and making strategic changes where necessary. In short, web crawling — and your site’s crawlability — is important to your business’s success.

How does a Web Crawler work?

Web crawlers start from a list of known URLs and crawl these web pages first. After this, web crawlers find hyperlinks to other URLs, and the next step is to crawl them. As a result, this process can be endless. This is why web crawlers will follow particular rules. For example, what pages to crawl, when they should crawl these pages again to check for content updates, and much more.

Furthermore, web crawler bots can be used by companies that need to gather data for their purposes. In this case, a web crawler is usually accompanied by a web scraper that downloads, or scrapes, required information. Note, that web scraping and web crawling are not the same, as scraping aims to parse and extract data from a website while the web crawling process is more focused on discovering target URLs. We have a dedicated crawler vs scraper blogspot discussing the topic in great detail, so if you’re curious to learn more, check it out.

Another crucial aspect to look out for is web crawler speeds. If your requirements are high, and you wish to crawl, let’s say a hundred thousand pages, very few web crawlers will be able to achieve your data-gathering needs, especially in a quick manner. Furthermore, crawling multiple threads at high speeds may break the server of the page you’re crawling, thus impacting the owners of said server and your own projects. Therefore, ensuring your web crawling tools are used ethically is beneficial for everyone and should be a top priority. Sometimes to mitigate crawling through entire threads of a website, a robot.txt file gets introduced to direct crawlers as to which pages ought to be crawled and how frequently.

Why Web Crawlers are important for SEO

Search engine optimization (SEO) is the process of improving a website to increase its visibility when people search for products or services. If a website has errors that make it difficult to crawl, or it can’t be crawled, its search engine results page (SERP) rankings will be lower or it won’t show up in organic search results. This is why it’s important to ensure webpages don’t have broken links or other errors and to allow web crawler bots to access websites and not block them.

Likewise, pages that aren’t crawled regularly won’t reflect any updated changes that may otherwise increase SEO. Regular crawling and ensuring that pages are updated can help improve SEO, especially for time-sensitive content.

What are the types of web crawlers?

There are four basic types of web crawlers.

  • Focused web crawlers search, index, and download web content concerning specific topics. Rather than exploring every hyperlink on a page as a standard web crawler would, a focused web crawler only follows links perceived to be relevant.
  • Incremental crawlers revisit websites to refresh an index and update URLs.
  • Parallel crawlers run multiple crawling processes at the same time to maximize the download rate.
  • Distributed crawlers use multiple crawlers to simultaneously index different sites.

web crawler

The challenges of Web Crawler

Database freshness

Websites’ content is updated regularly. Dynamic web pages, for example, change their content based on the activities and behaviors of visitors. This means that the website’s source code does not remain the same after you crawl the website. To provide the most up-to-date information to the user, the web crawler must re-crawl those web pages more frequently.

Crawler traps

Websites employ different techniques, such as crawler traps, to prevent web crawlers from accessing and crawling certain web pages. A crawler trap, or spider trap, causes a web crawler to make an infinite number of requests and become trapped in a vicious crawling circle. Websites may also unintentionally create crawler traps. In any case, when a crawler encounters a crawler trap, it enters something like an infinite loop that wastes the crawler’s resources.

Network Bandwidth

Downloading a large number of irrelevant web pages, utilizing a distributed web crawler, or recrawling many web pages all result in a high rate of network capacity consumption.

Duplicate pages

Web crawler bots mostly crawl all duplicate content on the web; however, only one version of a page is indexed. Duplicate content makes it difficult for search engine bots to determine which version of duplicate content to index and rank. When Googlebot discovers a group of identical web pages in a search result, it indexes and selects only one of these pages to display in response to a user’s search query.


Web crawlers are an important tool for today’s web infrastructure: They help users find relevant information more easily; they allow businesses to gather information about their competitors, such as pricing and product offerings; they enable data scientists and researchers to collect large amounts of data for analysis and research purposes.


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