How Web Crawling Worksprxcompass
What is Web Crawling? How it works in 2021 & Examples
- HTTP & SOCKS
- Price $1.3/IP
- Locations: DE, RU, US
- 5% OFF coupon: APFkysWLpG
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.
- HTTP & SOCKS
- Price $1.3/IP
- Locations: DE, RU, US
- 5% OFF coupon: APFkysWLpG
What is a web crawler? | How web spiders work | Cloudflare
What is a web crawler bot?
A web crawler, spider, or search engine bot downloads and indexes content from all over the Internet. The goal of such a bot is to learn what (almost) every webpage on the web is about, so that the information can be retrieved when it’s needed. They’re called “web crawlers” because crawling is the technical term for automatically accessing a website and obtaining data via a software program.
These bots are almost always operated by search engines. By applying a search algorithm to the data collected by web crawlers, search engines can provide relevant links in response to user search queries, generating the list of webpages that show up after a user types a search into Google or Bing (or another search engine).
A web crawler bot is like someone who goes through all the books in a disorganized library and puts together a card catalog so that anyone who visits the library can quickly and easily find the information they need. To help categorize and sort the library’s books by topic, the organizer will read the title, summary, and some of the internal text of each book to figure out what it’s about.
However, unlike a library, the Internet is not composed of physical piles of books, and that makes it hard to tell if all the necessary information has been indexed properly, or if vast quantities of it are being overlooked. To try to find all the relevant information the Internet has to offer, a web crawler bot will start with 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.
It is unknown how much of the publicly available Internet is actually crawled by search engine bots. Some sources estimate that only 40-70% of the Internet is indexed for search – and that’s billions of webpages.
What is search indexing?
Search indexing is like creating a library card catalog for the Internet so that a search engine knows where on the Internet to retrieve information when a person searches for it. It can also be compared to the index in the back of a book, which lists all the places in the book where a certain topic or phrase is mentioned.
Indexing focuses mostly on the text that appears on the page, and on the metadata* about the page that users don’t see. When most search engines index a page, they add all the words on the page to the index – except for words like “a, ” “an, ” and “the” in Google’s case. When users search for those words, the search engine goes through its index of all the pages where those words appear and selects the most relevant ones.
*In the context of search indexing, metadata is data that tells search engines what a webpage is about. Often the meta title and meta description are what will appear on search engine results pages, as opposed to content from the webpage that’s visible to users.
How do web crawlers work?
The Internet is constantly changing and expanding. Because it is not possible to know how many total webpages there are on the Internet, web crawler bots start from a seed, or a list of known URLs. They crawl the webpages at those URLs first. As they crawl those webpages, they will find hyperlinks to other URLs, and they add those to the list of pages to crawl next.
Given the vast number of webpages on the Internet that could be indexed for search, this process could go on almost indefinitely. However, a web crawler will follow certain policies that make it more selective about which pages to crawl, in what order to crawl them, and how often they should crawl them again to check for content updates.
The relative importance of each webpage: Most web crawlers don’t crawl the entire publicly available Internet and aren’t intended to; instead they decide which pages to crawl first based on the number of other pages that link to that page, the amount of visitors that page gets, and other factors that signify the page’s likelihood of containing important information.
The idea is that a webpage that is cited by a lot of other webpages and gets a lot of visitors is likely to contain high-quality, authoritative information, so it’s especially important that a search engine has it indexed – just as a library might make sure to keep plenty of copies of a book that gets checked out by lots of people.
Revisiting webpages: Content on the Web is continually being updated, removed, or moved to new locations. Web crawlers will periodically need to revisit pages to make sure the latest version of the content is indexed.
requirements: Web crawlers also decide which pages to crawl based on the protocol (also known as the robots exclusion protocol). Before crawling a webpage, they will check the file hosted by that page’s web server. A file is a text file that specifies the rules for any bots accessing the hosted website or application. These rules define which pages the bots can crawl, and which links they can follow. As an example, check out the file.
All these factors are weighted differently within the proprietary algorithms that each search engine builds into their spider bots. Web crawlers from different search engines will behave slightly differently, although the end goal is the same: to download and index content from webpages.
Why are web crawlers called ‘spiders’?
The Internet, or at least the part that most users access, is also known as the World Wide Web – in fact that’s where the “www” part of most website URLs comes from. It was only natural to call search engine bots “spiders, ” because they crawl all over the Web, just as real spiders crawl on spiderwebs.
Should web crawler bots always be allowed to access web properties?
That’s up to the web property, and it depends on a number of factors. Web crawlers require server resources in order to index content – they make requests that the server needs to respond to, just like a user visiting a website or other bots accessing a website. Depending on the amount of content on each page or the number of pages on the site, it could be in the website operator’s best interests not to allow search indexing too often, since too much indexing could overtax the server, drive up bandwidth costs, or both.
Also, developers or companies may not want some webpages to be discoverable unless a user already has been given a link to the page (without putting the page behind a paywall or a login). One example of such a case for enterprises is when they create a dedicated landing page for a marketing campaign, but they don’t want anyone not targeted by the campaign to access the page. In this way they can tailor the messaging or precisely measure the page’s performance. In such cases the enterprise can add a “no index” tag to the landing page, and it won’t show up in search engine results. They can also add a “disallow” tag in the page or in the file, and search engine spiders won’t crawl it at all.
Website owners may not want web crawler bots to crawl part or all of their sites for a variety of other reasons as well. For instance, a website that offers users the ability to search within the site may want to block the search results pages, as these are not useful for most users. Other auto-generated pages that are only helpful for one user or a few specific users should also be blocked.
What is the difference between web crawling and web scraping?
Web scraping, data scraping, or content scraping is when a bot downloads the content on a website without permission, often with the intention of using that content for a malicious purpose.
Web scraping is usually much more targeted than web crawling. Web scrapers may be after specific pages or specific websites only, while web crawlers will keep following links and crawling pages continuously.
Also, web scraper bots may disregard the strain they put on web servers, while web crawlers, especially those from major search engines, will obey the file and limit their requests so as not to overtax the web server.
How do web crawlers affect SEO?
SEO stands for search engine optimization, and it is the discipline of readying content for search indexing so that a website shows up higher in search engine results.
If spider bots don’t crawl a website, then it can’t be indexed, and it won’t show up in search results. For this reason, if a website owner wants to get organic traffic from search results, it is very important that they don’t block web crawler bots.
What web crawler bots are active on the Internet?
The bots from the major search engines are called:
Google: Googlebot (actually two crawlers, Googlebot Desktop and Googlebot Mobile, for desktop and mobile searches)
Yandex (Russian search engine): Yandex Bot
Baidu (Chinese search engine): Baidu Spider
There are also many less common web crawler bots, some of which aren’t associated with any search engine.
Why is it important for bot management to take web crawling into account?
Bad bots can cause a lot of damage, from poor user experiences to server crashes to data theft. However, in blocking bad bots, it’s important to still allow good bots, such as web crawlers, to access web properties. Cloudflare Bot Management allows good bots to keep accessing websites while still mitigating malicious bot traffic. The product maintains an automatically updated allowlist of good bots, like web crawlers, to ensure they aren’t blocked. Smaller organizations can gain a similar level of visibility and control over their bot traffic with Super Bot Fight Mode, available on Cloudflare Pro and Business plans.
Web crawler – ScienceDaily
Getting Up to Speed on the Proton
Oct. 6, 2021 — A century ago, scientists first detected the proton in the atomic nucleus. Yet, much about its contents remains a mystery. Scientists report a new theory for understanding what’s inside protons…
Intelligence Emerging from Random Polymer Networks
Oct. 6, 2021 — A team of researchers assembled a sulfonated polyaniline (SPAN) organic electrochemical network device (OEND) for use in reservoir computing. SPAN was deposited on gold electrodes which formed a…
Skyrmion Research: Braids of Nanovortices Discovered
Oct. 6, 2021 — A team of scientists has discovered a new physical phenomenon: complex braided structures made of tiny magnetic vortices known as skyrmions. Skyrmions were first detected experimentally a little over…
Making Self-Driving Cars Human-Friendly
Oct. 4, 2021 — Automated vehicles could be made more pedestrian-friendly thanks to new research which could help them predict when people will cross the road. Scientists investigating how to better understand…
Smuggling Light Through Opaque Materials
Oct. 5, 2021 — Electrical engineers have discovered that changing the physical shape of a class of materials commonly used in electronics can extend their use into the visible and ultraviolet parts of the…
A Robot That Finds Lost Items
Oct. 5, 2021 — Researchers developed a fully-integrated robotic arm that fuses visual data from a camera and radio frequency (RF) information from an antenna to find and retrieve object, even when they are buried…
Frequently Asked Questions about how web crawling works
How does a web crawler work?
Because it is not possible to know how many total webpages there are on the Internet, web crawler bots start from a seed, or a list of known URLs. They crawl the webpages at those URLs first. As they crawl those webpages, they will find hyperlinks to other URLs, and they add those to the list of pages to crawl next.
What is Web crawling used for?
Web crawlers are mainly used to create a copy of all the visited pages for later processing by a search engine, that will index the downloaded pages to provide fast searches. Crawlers can also be used for automating maintenance tasks on a Web site, such as checking links or validating HTML code.
Is Web crawling bad?
If you’re doing web crawling for your own purposes, it is legal as it falls under fair use doctrine. The complications start if you want to use scraped data for others, especially commercial purposes. … As long as you are not crawling at a disruptive rate and the source is public you should be fine.Jul 17, 2019