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What is a web crawler and how does it work

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What Is A Web Crawler And How Does It Work

While search engines are the modern gateway to access any information across the globe, web crawlers, their lesser-known sidekick, play a critical role in rounding up online content and form an integral part of the search engine optimization (SEO) strategy.

When it comes to technical SEO, it can often be difficult to understand how it actually functions. When searching for something on Google or other search engine platforms, you must have often wondered, how does the platform know where to look for the query?

The answer to this is ‘web crawlers’

Web crawlers search the web and index web pages to provide relevant results to the users online. In this blog, we will explore what web crawlers are, how they function, and why they crawl a website.

1] What is a Web Crawler?

A web crawler, also referred to as a search engine or web spider, is a type of bot operated by different search engines like Google and Bing. The purpose of a web crawler is to index the content available on the websites across the Internet so that the websites appear in search engine results.

Since search engines do not know what websites exist on the Internet, a program or a bot crawls and indexes pages so it can deliver the right results for keywords and phrases. Web crawlers are often operated by search engines within their algorithms. The algorithm is employed to instruct the web crawler about ways to find relevant data in response to a search (user) query.

A website owner or an SEO marketer can tell the website crawler not to crawl certain web pages on their websites by using a “noindex” metatag.

1.1] Search engines and crawlers

When searching on search engine platforms like Google or Bing using a keyword, the search engine sifts through thousands of pages to generate a well-defined and relevant list of results connected to that term.

But, how do these search engines have answers to all of these pages on file? How do they know where to look for them? And how can they generate these results within seconds?

The answer to this is web crawlers or spiders.

A search engine’s web crawler does not crawl the entire internet. Instead, it decides the significance of each web page based on specific factors, including the number of other pages linked to that page, page views and brand authority.

  • A web crawler is used to determine which pages to crawl, in what order should the page be crawled, and how often to crawl for updates.
  • Web crawlers build and store copies of these web pages in the engine’s database. This allows the user to make instant searches. It is also the reason why search engines often incorporate cached versions of websites.

2] How does a Web Crawler work?

Web crawlers crawl search engines or visit sites by passing between the links. However, if there is a new website without links connecting the pages to others, the user can ask search engines to conduct a website crawl by submitting the URL on Google Search Console.

In search engine land, crawlers act as explorers. They are always in search of discoverable links on web pages and jot them down in their algorithm or map them once they can understand their features. However, website crawlers can only sift through public web pages. Private web pages that a crawler cannot crawl are labelled as the dark web.

  • Web crawlers, when on a web page, gather data related to the page, including the copy as well as meta tags.
  • The crawlers then store the data pages in the index for Google’s algorithm to sort them for their contained keywords to later fetch and rank.

The basic route that a web crawler usually take is as follows:

  • Go to a website, for example: Mamba Media
  • Extract URLs linked in the web pages and add them to the list
  • Continue visiting the newly added/created pages

By visiting multiple web pages constantly, web crawlers can discover new pages or URLs, note the changes in the existing pages, and mark dead links.

3] Significance of Web Crawler for SEO

The way a search robot crawls a website affects how the web pages are indexed and how it is shown in the search results. This is what an SEO professional cares about.

  • Crawling is the first-way search engines lock onto these web pages. Improving the site for better ranking includes web pages that should be reachable and readable for web crawlers.
  • Regular crawling assists in displaying changes made by the website owner and ensures that the content is up-to-date.

However, crawling goes beyond the beginning of the SEO campaign. The website owner or SEO professional should consider web crawler behaviour as a measure to appear in search results as well as to enhance the user experience. If the ultimate goal of a business is to get more organic traffic from search engines, they should ensure that their website is being crawled.

3.1] Web Crawling Budget Management

Web crawling makes it easier for websites to rank in search engine results pages for newly published web pages. However, a website does not have unlimited crawling from Google or other search engines.

Google provides a crawl budget that tells the web crawler bots:

  • When to crawl
  • Which pages to crawl
  • How often to crawl pages
  • How much server pressure will be acceptable

To keep your site running smoothly, you need to adjust your web crawl rate limit and the crawl demand in Google Search Console.

  • The crawl rate limit indicates the maximum fetching rate (for any given site). The limit tells Googlebot when to crawl and the time to wait between fetches, so the load speed does not suffer or result in site errors. You can alter this in Google Search Console if you experience issues with Googlebot.
  • The crawl demand indicates the level of interest Google and its users have in a specific website. If the website does not have a huge following yet, then Googlebot will likely not crawl the site as often as the highly popular ones.

3.2] Roadblocks for Web Crawlers

With crawler roadblocks, the website owner or SEO marketer can protect sensitive, redundant, and irrelevant pages from appearing for specific keywords on search engines.

  • The first roadblock on this crawling journey is the noindex meta tag, which prohibits search engines from indexing as well as ranking a particular page.
  • Another known crawler roadblock is the robots.txt file. While this directive is not definitive, as crawlers can disobey the robots.txt files, it is handy for controlling the crawl budget.

4] Examples of Web Crawlers

Now that we know what a web crawler is and how it functions, let’s see some examples of web crawlers. Some search engines have fewer web crawlers or spiders. Larger search engines, however, employ multiple crawlers with specific focuses.

  • Google has its main crawler known as Googlebot, which encompasses mobile and desktop crawling.
  • Other web crawler bots available for Google are Googlebot Images, Googlebot News, Googlebot Videos, and AdsBot.
  • Even Bing has its standard web crawler known as Bingbot.

Here we have listed a handful of other web crawlers:

  • DuckDuckBot for DuckDuckGo
  • Yandex Bot for Yandex
  • Baiduspider for Baidu


Search engine crawlers are powerhouses when it comes to finding and recording website pages. They form the foundational building block for any SEO strategy as they enable the SEO company to fill in the gaps and offer businesses a robust campaign to not only boost their traffic but also their revenue and rankings.

Web crawlers are responsible for searching and indexing content online for search engines. They work to sort and filter through existing web pages for the search engines to understand what every web page is about. However, understanding web crawlers is just one element of effective technical SEO that can enable organisations to enhance their website’s performance.

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