What is Web Crawling? How it works in 2021 & Examples
Have you ever wondered how search engines such as Google and Bing collect all the data they present in their search results? It is because search engines index all the pages in their archives so that they can return the most relevant results based on queries. Web crawlers enable search engines to handle this process.
This article highlights important aspects of what crawling is, why it matters, how it works, applications & examples.
What is web crawling?
Web crawling is the process of indexing data on web pages by using a program or automated script. These automated scripts or programs are known by multiple names, including web crawler, spider, spider bot, and often shortened to crawler.
Web crawlers copy pages for processing by a search engine, which indexes the downloaded pages so that users can search more efficiently. The goal of a crawler is to learn what webpages are about. This enables users to retrieve any information on one or more pages when it’s needed.
Why is web crawling important?
Thanks to digital revolution, the total amount of data on the web has increased. In 2013, IBM stated that 90% of the world’s data had been created in the previous 2 years alone, and we continue to double the rate of data production every 2 years. Yet, almost 90% of data is unstructured, and web crawling is crucial to index all these unstructured data for search engines to provide relevant results.
According to Google data, interest in the web crawler topic has decreased since 2004. Yet, at the same time period, interest in web scraping has outpaced the interest in web crawling. Various interpretations can be made, some are:
Increasing interest in analytics and data-driven decision making are the main drivers for companies to invest in scraping.
Crawling done by search engines is no longer a topic of increasing interest since they have done this since the early 2000s
Search engine industry is a mature industry dominated by Google and Baidu, so few companies need to build crawlers.
How does a web crawler work?
Web crawlers start their crawling process by downloading the website’s file. The file includes sitemaps that list the URLs that the search engine can crawl. Once web crawlers start crawling a page, they discover new pages via links. These crawlers add newly discovered URLs to the crawl queue so that they can be crawled later. Thanks to these techniques, web crawlers can index every single page that is connected to others.
Since pages change regularly, it is also important to identify how frequently search engines should crawl them. Search engine crawlers use several algorithms to decide factors such as how often an existing page should be re-crawled and how many pages on a site should be indexed.
What are web crawling applications?
Web crawling is commonly used to index pages for search engines. This enables search engines to provide relevant results for queries. Web crawling is also used to describe web scraping, pulling structured data from web pages, and web scraping has numerous applications.
What are the examples of web crawling?
All search engines need to have crawlers, some examples are:
Amazonbot is an Amazon web crawler for web content identification and backlink discovery.
Baiduspider for Baidu
Bingbot for Bing search engine by Microsoft
DuckDuckBot for DuckDuckGo
Exabot for French search engine Exalead
Googlebot for Google
Yahoo! Slurp for Yahoo
Yandex Bot for Yandex
In addition to these, vendors like Bright Data enable companies to set up and scale web crawling operations rapidly with a SaaS model.
If you have questions about web crawling vendors, feel free to check out our sortable, updated, and transparent vendor list or contact us:
Let us find the right vendor for your business
Cem founded AIMultiple in 2017. Throughout his career, he served as a tech consultant, tech buyer and tech entrepreneur. He advised enterprises on their technology decisions at McKinsey & Company and Altman Solon for more than a decade. During his secondment, he led the technology strategy of a regional telco while reporting to the CEO. He has also led commercial growth of AI companies that reached from 0 to 7 figure revenues within months. Cem regularly speaks at international conferences on artificial intelligence and machine learning. He graduated from Bogazici University as a computer engineer and holds an MBA from Columbia Business School.
Crawl | Definition of Crawl by Merriam-Webster
crawled; crawling; crawls
1a: to move on one’s hands and knees
The baby crawled toward her mother.
b: to move slowly in a prone position without or as if without the use of limbs
The snake crawled into its hole. The soldiers crawled forward on their bellies.
2: to move or progress slowly or laboriously
traffic crawling along at 10 miles an hour
3: to advance by guile or servility
crawling into favor by toadying to his boss
4: to spread by extending stems or tendrils
a crawling vine
5a: to be alive or swarming with or as if with creeping things
a kitchen crawling with ants
b: to have the sensation of insects creeping over one
the story made her flesh crawl
6: to fail to stay evenly spread
—used of paint, varnish, or glaze
1: to move upon in or as if in a creeping manner
all the creatures that crawl the earth
2: to reprove harshly
they got no good right to crawl me for what I wrote— Marjorie K. Rawlings
1a: the act or action of crawling
b: slow or laborious progress
chiefly British: a going from one pub to another
2: a fast swimming stroke executed in a prone position with alternating overarm strokes and a flutter kick
3: lettering that moves vertically or horizontally across a television or motion-picture screen to give information (such as performer credits or news bulletins)
What is a web crawler and how does it work? – Ryte
A crawler is a computer program that automatically searches documents on the Web. Crawlers are primarily programmed for repetitive actions so that browsing is automated. Search engines use crawlers most frequently to browse the internet and build an index. Other crawlers search different types of information such as RSS feeds and email addresses. The term crawler comes from the first search engine on the Internet: the Web Crawler. Synonyms are also “Bot” or “Spider. ” The most well known webcrawler is the Googlebot.
1 How does a crawler work?
3 Examples of a crawler
4 Crawler vs. Scraper
5 Blocking a crawler
6 Significance for search engine optimization
8 Web Links
How does a crawler work? 
In principle, a crawler is like a librarian. It looks for information on the Web, which it assigns to certain categories, and then indexes and catalogues it so that the crawled information is retrievable and can be evaluated.
The operations of these computer programs need to be established before a crawl is initiated. Every order is thus defined in advance. The crawler then executes these instructions automatically. An index is created with the results of the crawler, which can be accessed through output software.
The information a crawler will gather from the Web depends on the particular instructions.
This graphic visualize the link relationships that are uncovered by a crawler:
The classic goal of a crawler is to create an index. Thus crawlers are the basis for the work of search engines. They first scour the Web for content and then make the results available to users. Focused crawlers, for example, focus on current, content-relevant websites when indexing.
Web crawlers are also used for other purposes:
Price comparison portals search for information on specific products on the Web, so that prices or data can be compared accurately.
In the area of data mining, a crawler may collect publicly available e-mail or postal addresses of companies.
Web analysis tools use crawlers or spiders to collect data for page views, or incoming or outbound links.
Crawlers serve to provide information hubs with data, for example, news sites.
Examples of a crawler
The most well known crawler is the Googlebot, and there are many additional examples as search engines generally use their own web crawlers. For example
Crawler vs. Scraper
Unlike a scraper, a crawler only collects and prepares data. Scraping is, however, a black hat technique, which aims to copy data in the form of content from other sites to place it that way or a slightly modified form of it on one’s own website. While a crawler mostly deals with metadata that is not visible to the user at first glance, a scraper extracts tangible content.
Blocking a crawler
If you don’t want certain crawlers to browse your website, you can exclude their user agent using However, that cannot prevent content from being indexed by search engines. The noindex meta tag or the canonical tag serves better for this purpose.
Significance for search engine optimization
Webcrawlers like the Googlebot achieve their purpose of ranking websites in the SERP through crawling and indexing. They follow permanent links in the WWW and on websites. Per website, every crawler has a limited timeframe and budget available. Website owners can utilize the crawl budget of the Googlebot more effectively by optimizing the website structure such as the navigation. URLs deemed more important due to a high number of sessions and trustworthy incoming links are usually crawled more often. There are certain measures for controlling crawlers like the Googlebot such as the, which can provide concrete instructions not to crawl certain areas of a website, and the XML sitemap. This is stored in the Google Search Console, and provides a clear overview of the structure of a website, making it clear which areas should be crawled and indexed.
↑ Web Crawlers. Accessed on May 28, 2019
Google Support – Googlebot
Frequently Asked Questions about web crawlers eg
What is crawling with example?
We got down on our knees and crawled through a small opening. The baby crawled across the floor toward her mother. The soldiers crawled forward on their bellies. The snake crawled into its hole.
Who are crawlers give two examples?
Examples of a crawlerBingbot.Slurp Bot.DuckDuckBot.Baiduspider.Yandex Bot.Sogou Spider.Exabot.Alexa Crawler.
What are web crawling tools?
A web crawler, or spider, is a type of bot that is typically operated by search engines like Google and Bing. Their purpose is to index the content of websites all across the Internet so that those websites can appear in search engine results.