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Exploring the Role of Search Engine Bots and Crawlers

Last Updated : 25 Oct, 2023
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The World Wide Web is frequently browsed by automated programs known as spiders, crawlers, and search engine bots. They are used by search engines to find recently updated material as well as to index it so that users can find it when they do a search.

Crawling is the process of viewing websites and clicking on connections to other websites. Crawlers begin by obtaining a list of URLs from several sources, including sitemaps, links from other websites, and the robots.txt file on each website. Afterward, they go to each of these URLs and click the links on the corresponding sites to find fresh URLs. This procedure keeps going until the crawler has covered a sizeable chunk of the web. A crawler visits a website, extracts the information, and then stores the content in a database. The search engine uses this database, which it refers to as the index, to obtain results when users do a search.

How Do Search Engines Work?

Search engines use web crawlers to find and index recent data. When a user submits a search query, the search engine searches its database for the results that are most relevant and ranks them according to a number of criteria. A search engine’s objective is to deliver the most pertinent results to users’ queries as quickly as possible. All search engines, in general, go through three stages:

  • Crawling
  • Indexing
  • Ranking and Retrieval

What is search engine crawling?

Search engine crawling is the technique used by search engines to visit websites and go via links to other websites. Crawlers, commonly referred to as spiders or bots, are used by search engines to browse the web. Crawlers begin by obtaining a list of URLs from several sources, including sitemaps, links from other websites, and the robots.txt file on each website. Afterward, they go to each of these URLs and click the links on the corresponding sites to find fresh URLs. This procedure keeps going until the bot has thoroughly crawled the internet. A crawler visits a website, extracts the information, and then stores the content in a database. The search engine uses this database, which it refers to as the index, to obtain results when users do a search.

A crucial component of how search engines operate is crawling. It enables search engines to find fresh and updated information and to index it, making it accessible to users when they do searches.

Example: Consider a library that must maintain a record of every book in its holdings. A librarian patrols the library’s shelves, inspecting each book as she passes. Each book’s title, author, and other details are entered by the librarian into a database. The index of a search engine is similar to this database. All of the web pages that the search engine has crawled are described there. The search engine scans the index when a user types in a query to determine which results are most pertinent. Crawlers enable search engines to find fresh and updated material, index it, and make it accessible to users when they do searches.

How do web crawlers work?

A web crawler, commonly referred to as a web spider or web bot, uses a set of guidelines and algorithms to choose which internet pages to scan. Choosing which pages to crawl is sometimes referred to as “URL selection” or “URL prioritization.” The following are some of the crucial elements and techniques that web spiders consider while making this choice:

1. Seed URLs

Web crawlers begin by using a list of seed URLs that their operators supply. The crawl will normally start at these seed URLs, and the crawler will first fetch and examine the content of these sites.

2. Robots.txt

Web crawlers check the `robots.txt` file of a website before crawling it. The `robots.txt` file contains instructions from the website owner about which parts of the site should not be crawled. The crawler will respect these rules and avoid crawling disallowed pages.

3. Domain and Subdomain Prioritization

Crawlers frequently give priority to certain domains or subdomains when crawling websites. In contrast to lesser-known or lower-quality domains, high-quality and authoritative domains may be crawled more frequently.

4. Page Freshness

Some crawlers give pages that have recently changed or updated priority. To decide which pages to crawl more regularly, they may utilize signals like the time since the previous alteration or the frequency of updates.

5. Page Importance

Web crawlers assess the importance of a page based on factors like its inbound and outbound links, page authority, and relevance to specific topics or keywords. Important pages are crawled more often.

6. Page Depth

Both a depth-first and a breadth-first strategy can be used by crawlers. Prior to moving on to other websites, depth-first crawlers give priority to pages that are further down in the website’s hierarchy. Crawlers that focus on breadth attempt to visit a variety of pages on various websites.

7. URL Discovery

When web crawlers explore connections from previously inspected sites, they frequently discover new URLs to crawl. In order to find URLs, they can also employ sitemaps that website owners supply.

8. URL Queuing and Prioritization

Crawlers keep a list of URLs they want to visit. Based on the aforementioned criteria, including significance, freshness, and relevancy, they prioritize URLs. URLs with a high priority are crawled first.

9. Recrawling

At regular intervals, web crawlers return to previously crawled pages to look for changes. Depending on variables like page significance and update frequency, recrawling frequency may change.

10. Politeness

In order to prevent flooding websites with requests, crawlers often adhere to a set of courtesy guidelines. To be considerate of a website’s resources, they could add delays between requests and restrict the amount of queries made per second.

Note: In order to efficiently search and index web content while adhering to the guidelines and resource constraints of website owners, web crawlers continuously alter and enhance their crawling strategies. Different web crawling algorithms and criteria may be used by different crawling efforts and organizations.

Web Crawlers Bots

  • Amazonbot
  • Bingbot
  • DuckDuckBot
  • Googlebot
  • Yahoo Slurp
  • Yandex Bot

Why are web crawlers referred to as “spiders”?

Web crawlers are known as “spiders” because of the way they browse the internet, which is akin to how spiders browse their webs. After beginning at a central location, spiders spread out in all directions while following the threads they come across. Web crawlers also begin at a central location—typically a list of well-known URLs—and proceed to follow any connections they come across on those sites.

Web crawlers are also referred to as “spiders” for the following reasons:

  1. Both spiders and web crawlers are quite proficient at traversing their respective webs.
  2. Web crawlers are excellent at discovering new links to follow, and spiders are excellent at finding new threads to follow.
  3. Web crawlers are particularly adept at avoiding becoming caught in endless loops, much as spiders are highly good at avoiding getting caught in their webs.

Difference between Web Scraping and Web Crawling

Web crawling and web scraping are two similar methods for gathering information from the internet. Some important differences are given below:

  • Web crawling focuses on finding fresh and updated material on the web, whereas web scraping concentrates on obtaining particular data from websites.
  • Web crawling is used by search engines to index the web and by other websites to collect data, whereas web scraping is frequently used to collect data for market research, pricing comparison, and other reasons.
  • Web crawling is a constant and continuing operation. Web crawlers from search engines visit websites on a regular basis to maintain their indexes up to date, whereas web scraping is often conducted as a one-time or periodic operation, targeting specific data at a certain point in time.

Should web crawling be allowed on any specific webpage?

The decision to enable web crawling on a certain webpage is based on a number of factors, including the rights and interests of both the website owner and the web crawler operator.


  • Indexing and Visibility: Making a website crawlable may make it visible to search engines, which is advantageous for websites looking to increase traffic and visibility. The likelihood of a website showing up in search engine results pages (SERPs) can be increased.
  • Accessibility: By using web crawlers to access material through screen readers and other assistive technology, web crawling can make a webpage’s content accessible to a larger audience, including those with disabilities.
  • Content Sharing: Web crawling enables material to be shared and disseminated more broadly online, thus broadening its appeal and effect.
  • Research and Analysis: Web crawling may be used by researchers, data analysts, and developers to acquire information, carry out studies, or produce ground-breaking applications that advance society.


  • Security and privacy concerns: Some website owners may be worried about their material being scraped or indexed without their permission, which can cause security and privacy problems.
  • Bandwidth and Server Load: Frequent and aggressive web crawling can load a website’s servers heavily and use a lot of bandwidth, which could have an impact on how well it performs and drive up hosting prices.
  • Intellectual property: Unauthorized web crawling may result in the unauthorized copyrighted information being reproduced and distributed, thus violating intellectual property rights.
  • Data Misuse and Scraping: Some web crawlers may exploit data for illegal activities like spamming, phishing, or fraud, which might be detrimental to both website owners and visitors.


Search engine bots and crawlers are essential for the web ecosystem. They contribute to making sure people can access the web and locate the information they require. On whether or not web crawling should be permitted on any specific webpage, there is some disagreement. Each website owner must ultimately decide whether or not to permit web crawling on their pages. To be clear, web crawling is an essential component of how the internet functions.

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