Webpage Crawler
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.
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 to Crawl a Website with Deepcrawl
Running frequent and targeted crawls of your website is a key part of improving it’s technical health and improving rankings in organic search. In this guide, you’ll learn how to a crawl a website efficiently and effectively with DeepCrawl. The six steps to crawling a website include:
Configuring the URL sources
Understanding the domain structure
Running a test crawl
Adding crawl restrictions
Testing your changes
Running your crawl
Step 1: Configuring the URL sources
There are six types of URL sources you can include in your DeepCrawl projects.
Including each one strategically, is the key to an efficient, and comprehensive crawl:
Web crawl: Crawl only the site by following its links to deeper levels.
Sitemaps: Crawl a set of sitemaps, and the URLs in those sitemaps. Links on these pages will not be followed or crawled.
Analytics: Upload analytics source data, and crawl the URLs, to discover additional landing pages on your site which may not be linked. The analytics data will be available in various reports.
Backlinks: Upload backlink source data, and crawl the URLs, to discover additional URLs with backlinks on your site. The backlink data will be available in various reports.
URL lists: Crawl a fixed list of URLs. Links on these pages will not be followed or crawled.
Log files: Upload log file summary data from log file analyser tools, such as Splunk and
Ideally, a website should be crawled in full (including every linked URL on the site). However, very large websites, or sites with many architectural problems, may not be able to be fully crawled immediately. It may be necessary to restrict the crawl to certain sections of the site, or limit specific URL patterns (we’ll cover how to do this below).
Step 2: Understanding the Domain Structure
Before starting a crawl, it’s a good idea to get a better understanding of your site’s domain structure:
Check the www/non-www and / configuration of the domain when you add the domain.
Identify whether the site is using sub-domains.
If you are not sure about sub-domains, check the DeepCrawl “Crawl Subdomains” option and they will automatically be discovered if they are linked.
Step 3: Running a Test Crawl
Start with a small “Web Crawl, ” to look for signs that the site is uncrawlable.
Before starting the crawl, ensure that you have set the “Crawl Limit” to a low quantity. This will make your first checks more efficient, as you won’t have to wait very long to see the results.
Problems to watch for include:
A high number of URLs returning error codes, such as 401 access denied
URLs returned that are not of the correct subdomain – check that the base domain is correct under “Project Settings”.
Very low number of URLs found.
A large number of failed URLs (502, 504, etc).
A large number of canonicalized URLs.
A large number of duplicate pages.
A significant increase in the number of pages found at each level.
To save time, and check for obvious problems immediately, download the URLs during the crawl:
Step 4: Adding Crawl Restrictions
Next, reduce the size of the crawl by identifying anything that can be excluded. Adding restrictions ensures you are not wasting time (or credits) crawling URLs that are not important to you. All the following restrictions can be added within the “Advanced Settings” tab.
Remove Parameters
If you have excluded any parameters from search engine crawls with URL parameter tools like Google Search Console, enter these in the “Remove Parameters” field under “Advanced Settings. ”
Add Custom Settings
DeepCrawl’s “Robots Overwrite” feature allows you to identify additional URLs that can be excluded using a custom file – allowing you to test the impact of pushing a new file to a live environment.
Upload the alternative version of your robots file under “Advanced Settings” and select “Use Robots Override” when starting the crawl:
Filter URLs and URL Paths
Use the “Included/Excluded” URL fields under “Advanced Settings” to limit the crawl to specific areas of interest.
Add Crawl Limits for Groups of Pages
Use the “Page Grouping” feature, under “Advanced Settings, ” to restrict the number of URLs crawled for groups of pages based on their URL patterns.
Here, you can add a name.
In the “Page URL Match” column you can add a regular expression.
Add a maximum number of URLs to crawl in the “Crawl Limit” column.
URLs matching the designated path are counted. When the limits have been reached, all further matching URLs go into the “Page Group Restrictions” report and are not crawled.
Step 5: Testing Your Changes
Run test “Web Crawls” to ensure your configuration is correct and you’re ready to run a full crawl.
Step 6: Running your Crawl
Ensure you’ve increased the “Crawl Limit” before running a more in-depth crawl.
Consider running a crawl with as many URL sources as possible, to supplement your linked URLs with XML Sitemap and Google Analytics, and other data.
If you have specified a subdomain of www within the “Base Domain” setting, subdomains such as blog or default, will not be crawled.
To include subdomains select “Crawl Subdomains” within the “Project Settings” tab.
Set “Scheduling” for your crawls and track your progress.
Handy Tips
Settings for Specific Requirements
If you have a test/sandbox site you can run a “Comparison Crawl” by adding your test site domain and authentication details in “Advanced Settings. ”
For more about the Test vs Live feature, check out our guide to Comparing a Test Website to a Live Website.
To crawl an AJAX-style website, with an escaped fragment solution, use the “URL Rewrite” function to modify all linked URLs to the escaped fragment format.
Read more about our testing features – Testing Development Changes Before Putting Them Live.
Changing Crawl Rate
Watch for performance issues caused by the crawler while running a crawl.
If you see connection errors, or multiple 502/503 type errors, you may need to reduce the crawl rate under “Advanced Settings. ”
If you have a robust hosting solution, you may be able to crawl the site at a faster rate.
The crawl rate can be increased at times when the site load is reduced – 4 a. m. for example.
Head to “Advanced Settings” > “Crawl Rate” > “Add Rate Restriction. ”
Analyze Outbound Links
Sites with a large quantity of external links, may want to ensure that users are not directed to dead links.
To check this, select “Crawl External Links” under “Project Settings, ” adding an HTTP status code next to external links within your report.
Read more on outbound link audits to learn about analyzing and cleaning up external links.
Change User Agent
See your site through a variety of crawlers’ eyes (Facebook/Bingbot etc. ) by changing the user agent in “Advanced Settings. ”
Add a custom user agent to determine how your website responds.
After The Crawl
Reset your “Project Settings” after the crawl, so you can continue to crawl with ‘real-world’ settings applied.
Remember, the more you experiment and crawl, the closer you get to becoming an expert crawler.
Start your journey with DeepCrawl
If you’re interested in running a crawl with DeepCrawl, discover our range of flexible plans or if you want to find out more about our platform simply drop us a message and we’ll get back to you asap.
Author
Sam Marsden
Sam Marsden is Deepcrawl’s Former SEO & Content Manager. Sam speaks regularly at marketing conferences, like SMX and BrightonSEO, and is a contributor to industry publications such as Search Engine Journal and State of Digital.
Frequently Asked Questions about webpage crawler
What is a web crawler used for?
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.
How do I crawl a website?
The six steps to crawling a website include:Understanding the domain structure.Configuring the URL sources.Running a test crawl.Adding crawl restrictions.Testing your changes.Running your crawl.
Which web crawler is best?
Top 20 web crawler tools to scrape the websitesCyotek WebCopy. WebCopy is a free website crawler that allows you to copy partial or full websites locally into your hard disk for offline reading. … HTTrack. … Octoparse. … Getleft. … Scraper. … OutWit Hub. … ParseHub. … Visual Scraper.More items…•Jun 3, 2017
