What Is a Web Crawler? How Spiders Help Your Website Work Better

What is a Web Crawler?

Table Of Content


A crawler, also known as a spider or bot, is a program used by search engines to scan and index web pages on the internet systematically.

It is harder for a search bot to determine whether all information has been properly indexed on the Internet, as opposed to a library, which has physical piles of books.

If the web crawler bot wishes to collect all the relevant information that the Internet has to offer, it begins by scanning a certain set of known webpages and then follow hyperlinks from those pages to other pages, follow hyperlinks from those other pages to additional pages, and so on.

Search engine bots do not crawl all of the websites that are publicly accessible. The Internet contains billions of web pages – but only 40-70% can be searched.

The purpose of search indexing

By establishing search indexing, a search engine can learn where on the Internet to find information when a user searches for it. It is similar to organizing a library card catalog for the Internet. An annotated bibliography may also be analogous to it, as it lists all references to a particular topic or phrase in the book.

Search engines use indexing primarily to locate content within pages and to identify data* about the pages that are not visible to users. In most cases, when a search engine indexes a page, it includes every word – except for articles like A, An and The in Google’s case. Search engines use an index of all pages that appear with those terms to select the most relevant ones when users use those words.

A webpage’s metadata describes what it contains to search engines as part of the indexing process. Often, what appears on search engine result pages are the meta title and meta description, rather than the visible content on a webpage.

How do web crawlers work?

Change and expansion are constants on the Internet. The seed, or list of known URLs, is used by web crawlers because it is impossible to know the total number of web pages on the Internet. Crawling starts with these URLs.

The crawlers find hyperlinks to various URLs as they crawl those webpages, and they include those URLs in their list of pages to crawl next.

Considering how many pages there are available on the internet for search, it would take a very long time to complete. Web crawlers, on the other hand, are programmed to follow certain policies that make it more selective about which pages to crawl, the order they should crawl them in, and how often they should crawl them to ensure they have not updated their content.

There is no general method for finding the relative importance of every webpage; instead, web crawlers choose which webpages to crawl first based on how many other pages link to that page, how many visitors the page receives, and other factors indicating the likelihood the page includes valuable information.

It’s important that a search engine indexes a webpage that gets a lot of traffic and is cited by a lot of other web pages, just as a library ensures that a popular book is available for checkout frequently.

Reviewing web pages: Web content constantly changes, disappears, or moves. Crawlers will periodically have to visit pages in order to index the most current versions of content.

The robots.txt protocol also dictates which pages to crawl: The process of crawling each page is determined by a robots.txt file. Prior to crawling a page, the search engine spiders check the robots.txt file on the webserver that controls that page.

Robots.txt files are used to specify what rules bots should follow if they access a website hosted on the server or even an application. Bots can follow these links and crawl these pages if they comply with these rules.

Each search engine makes their spider bots weigh these factors differently based on its own proprietary algorithm. Although the goal of search engine ‘web crawlers’ is to download and index content from web pages, they act differently depending on which search engine they are running.

What is the meaning of the word “spider” in web crawling

In fact, the “www” part of most website URLs refers to parts of the World Wide Web, or at least what most users access. As spiders crawl on spiderwebs, so too have search engine bots crawled worldwide on the Web.

The access of web crawler bots to web properties should always be allowed?

That depends on a number of factors, and is up to the web property. The server must respond to requests made by web crawlers in order to index content – just as a user or another bot accessing a website would.

The website operator may find it beneficial not to allow search indexing too often, depending on how much content is on each page, how many pages exist, or other factors. An excessive amount of indexing can overburden the server or drive up bandwidth costs.

Also, some organizations and developers may not want certain webpages to be accessible to users unless they have been given access to the page beforehand, here access means a link to the web page. Creating a landing page for a marketing campaign is an example of a case where enterprises do not want unauthorized individuals to access it.

They can use this information to tailor messages or precisely measure a page’s performance. Businesses can use “no-index” or a “tag” to block search engines from displaying their landing pages. The “disallow” tag or robots.txt file will prevent search engine spiders from crawling the page.

Numerous reasons exist for not wanting to have a website indexed by search engines. The search results pages on a website that allows users to search within its domain may be blocked since users are not interested in them. Additionally, there should also be a way to block automatically created pages that are only meant for a few specific users.

Web crawling vs. web scraping: which is better?

Web scraping, data scraping, or content scraping refers to the act of downloading content on a website without the webmaster’s consent, usually in order to use it maliciously.

Scraping of web pages is typically more targeted than web crawling. Website scrapers are focused on particular pages or websites, but web crawlers will keep crawling those pages forever.

Also, scrapers may ignore the burden placed on servers, while web crawlers, most notably search engine crawlers, observe the robots.txt file and make fewer requests to avoid overloading the server.

Does Web Crawling Affect SEO?

A website’s search engine ranking can be improved by search engine optimization, which prepares the content for search engine indexing.

Search engines do not index a website if spider bots haven’t crawled it. It is therefore very important that a website owner does not block web crawler bots if they want organic traffic from search results.

Which web crawler spiders are currently operating on the Internet?

The bots from the major search engines are called:

  • Google: Googlebot
  • Yandex (Russian search engine): Yandex Bot
  • Bing: Bingbot
  • Baidu (Chinese search engine): Baidu Spider

Aside from web crawler bots associated with search engines, there are several less common bots that crawl the Internet.

Finally, Web crawlers play an important role in understanding a website and its contents. Web spiders are an important aspect of search engines and how they communicate with our content.

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