How Web Crawler Works
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)
Bing: Bingbot
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.
How Google’s Site Crawlers Index Your Site – Google Search
Чтобы пользователи могли быстро найти нужные сведения, наши роботы собирают информацию на сотнях миллиардов страниц и упорядочивают ее в поисковом индексе.
Основы Google Поиска
При очередном сканировании наряду со списком веб-адресов, полученных во время предыдущего сканирования, используются файлы Sitemap, которые предоставляются владельцами сайтов. По мере посещения сайтов робот переходит по указанным на них ссылкам на другие страницы. Особое внимание он уделяет новым и измененным сайтам, а также неработающим ссылкам. Он самостоятельно определяет, какие сайты сканировать, как часто это нужно делать и какое количество страниц следует выбрать на каждом из них.
При помощи Search Console владельцы сайтов могут указывать, как именно следует сканировать их ресурсы, в частности предоставлять подробные инструкции по обработке страниц, запрашивать их повторное сканирование, а также запрещать сканирование, используя файл Google не увеличивает частоту сканирования отдельных ресурсов за плату. Чтобы результаты поиска были максимально полезными для пользователей, все владельцы сайтов получают одни и те же инструменты.
Поиск информации с помощью сканирования
Интернет похож на библиотеку, которая содержит миллиарды изданий и постоянно пополняется, но не располагает централизованной системой учета книг. Чтобы находить общедоступные страницы, мы используем специальное программное обеспечение, называемое поисковыми роботами. Роботы анализируют страницы и переходят по ссылкам на них – как обычные пользователи. После этого они отправляют сведения о ресурсах на серверы Google.
Систематизация информации с помощью индексирования
Во время сканирования наши системы обрабатывают материалы страниц так же, как это делают браузеры, и регистрируют данные по ключевым словам и новизне контента, а затем создают на их основе поисковый индекс.
Индекс Google Поиска содержит сотни миллиардов страниц. Его объем значительно превышает 100 миллионов гигабайт. Он похож на указатель в конце книги, в котором есть отдельная запись для каждого слова на всех проиндексированных страницах. Во время индексирования данные о странице добавляются в записи по всем словам, которые на ней есть.
Построение Сети Знаний — более современный способ определить интересы пользователей по сравнению с сопоставлением ключевых слов. Для этого мы упорядочиваем не только данные по страницам, но и другие типы информации. В настоящее время Google Поиск позволяет найти нужный фрагмент текста в миллионах книг из крупнейших библиотек, узнать расписание общественного транспорта, а также изучить данные общедоступных источников, таких как сайт Всемирного банка.
Web Crawler 101: What Is a Web Crawler? (And How It Works)
Have you ever wondered how answers can be at our fingertips in the digital age? It seems impossibly convenient to be able to type a question into a search bar and receive a list of helpful resources.
Search engines are the gateway of easy-access information, but web crawlers, their little-known sidekicks, play a crucial role in rounding up online content. Plus, they are essential to your search engine optimization (SEO) strategy.
“Ok, but what is a web crawler exactly? ” Dive into this web crawler explanation post to find out!
If you need to get your website crawled and at the top of Google, we have a team of SEO experts that can help at WebFX. We’ve driven over 255, 000 page-one rankings on Google for our clients!
Contact us online or call us at 888-601-5359 today to find out how we can transform your site performance.
What is a web crawler?
Web crawlers go by many names, including spiders, robots, and bots, and these descriptive names sum up what they do — they crawl across the World Wide Web to index pages for search engines.
Search engines don’t magically know what websites exist on the Internet. The programs have to crawl and index them before they can deliver the right pages for keywords and phrases, or the words people use to find a useful page.
Think of it like grocery shopping in a new store.
You have to walk down the aisles and look at the products before you can pick out what you need.
In the same way, search engines use web crawler programs as their helpers to browse the Internet for pages before storing that page data to use in future searches.
This analogy also applies to how crawlers travel from link to link on pages.
You can’t see what’s behind a can of soup on the grocery store shelf until you’ve lifted the can in front. Search engine crawlers also need a starting place — a link — before they can find the next page and the next link.
How does a web crawler work?
Search engines crawl or visit sites by passing between the links on pages. However, if you have a new website without links connecting your pages to others, you can ask search engines to crawl your site by submitting your URL on Google Search Console.
You can learn more about how to check if your site is crawlable and indexable in our video!
Crawlers act as explorers in a new land.
They’re always looking for discoverable links on pages and jotting them down on their map once they understand their features. But website crawlers can only sift through public pages on websites, and the private pages that they can’t crawl are labeled the “dark web. ”
Web crawlers, while they’re on the page, gather information about the page like the copy and meta tags. Then, the crawlers store the pages in the index so Google’s algorithm can sort them for their contained words to later fetch and rank for users.
What are some web crawler examples?
So, what are some examples of web crawlers?
Popular search engines all have a web crawler, and the large ones have multiple crawlers with specific focuses.
For example, Google has its main crawler, Googlebot, which encompasses mobile and desktop crawling. But there are also several additional bots for Google, like Googlebot Images, Googlebot Videos, Googlebot News, and AdsBot.
Here are a handful of other web crawlers you may come across:
DuckDuckBot for DuckDuckGo
Yandex Bot for Yandex
Baiduspider for Baidu
Yahoo! Slurp for Yahoo!
Bing also has a standard web crawler called Bingbot and more specific bots, like MSNBot-Media and BingPreview. Its main crawler used to be MSNBot, which has since taken a backseat for standard crawling and only covers minor crawl duties now.
Why web crawlers matter for SEO
SEO — improving your site for better rankings — requires pages to be reachable and readable for web crawlers. Crawling is the first way search engines lock onto your pages, but regular crawling helps them display changes you make and stay updated on your content freshness.
Since crawling goes beyond the beginning of your SEO campaign, you can consider web crawler behavior as a proactive measure for helping you appear in search results and enhance the user experience.
Keep reading to go over the relationship between web crawlers and SEO.
Crawl budget management
Ongoing web crawling gives your newly published pages a chance to appear in the search engine results pages (SERPs). However, you aren’t given unlimited crawling from Google and most other search engines.
Google has a crawl budget that guides its bots in:
How often to crawl
Which pages to scan
How much server pressure is acceptable
It’s a good thing there’s a crawl budget in place. Otherwise, the activity of crawlers and visitors could overload your site.
If you want to keep your site running smoothly, you can adjust web crawling through the crawl rate limit and the crawl demand.
The crawl rate limit monitors fetching on sites so that the load speed doesn’t suffer or results in a surge of errors. You can alter it in Google Search Console if you experience issues from Googlebot.
The crawl demand is the level of interest Google and its users have on your website. So, if you don’t have a wide following yet, then Googlebot isn’t going to crawl your site as often as highly popular ones.
Roadblocks for web crawlers
There are a few ways to block web crawlers from accessing your pages purposefully. Not every page on your site should rank in the SERPs, and these crawler roadblocks can protect sensitive, redundant, or irrelevant pages from appearing for keywords.
The first roadblock is the noindex meta tag, which stops search engines from indexing and ranking a particular page. It’s usually wise to apply noindex to admin pages, thank you pages, and internal search results.
Another crawler roadblock is the file. This directive isn’t as definitive because crawlers can opt-out of obeying your files, but it’s handy for controlling your crawl budget.
Need help with your SEO, marketing manager? Check out our SEO Guide for Marketing Managers to start driving more site traffic, leads, and revenue!
VIEW THE GUIDE
Optimize search engine crawling with WebFX
After covering the crawling basics, you should have an answer to your question, “What is a web crawler? ” Search engine crawlers are incredible powerhouses for finding and recording website pages.
This is a foundational building block for your SEO strategy, and an SEO company can fill in the gaps and provide your business with a robust campaign to boost traffic, revenue, and rankings in SERPs.
Named the #1 SEO firm in the world, WebFX is ready to drive real results for you. With clients from a range of industries, we have plenty of experience. But we can also say that our clients are thrilled with their partnership with us — read their 400+ testimonials to hear the details.
Are you ready to speak to an expert about our SEO services?
Contact us online or call us at 888-601-5359 today — we’d love to hear from you.
Frequently Asked Questions about how web crawler works
How does Google Web crawler work?
Finding information by crawling We use software known as web crawlers to discover publicly available webpages. Crawlers look at webpages and follow links on those pages, much like you would if you were browsing content on the web. They go from link to link and bring data about those webpages back to Google’s servers.
What is Web crawler example?
For example, Google has its main crawler, Googlebot, which encompasses mobile and desktop crawling. But there are also several additional bots for Google, like Googlebot Images, Googlebot Videos, Googlebot News, and AdsBot. Here are a handful of other web crawlers you may come across: DuckDuckBot for DuckDuckGo.Jul 11, 2019
Is it legal to crawl a website?
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
