What is a web crawler and how does it work | by Octoparse | March 2022
A web crawler, also known as a web spider or search engine robot, is a robot that visits and indexes the content of web pages anywhere on the Internet. With such a large amount of information, a search engine will be able to present its users’ relevant information in search results.
The goal of a web crawler is to get information, often to keep getting new information to feed a search engine.
If a search engine is a supermarket, what a web crawler does is like big sourcing – it visits different websites/webpages, navigates and stores information in its own warehouse. When a customer comes and asks for something, there will be certain products to offer on the shelves.
He is supplied by indexing web pages and the content they contain. The indexed content will be ready to be retrieved and when a user searches for a particular query, it can present the user with the most relevant information.
A web crawler is a super workhorse or it has to be. It’s not just because there is a huge number of new pages being created every minute in the world (about 252,000 new websites are created every day worldwide according to Siteefy), but also due to changes and updates to these pages.
Some web crawlers are active on the Internet:
They are primarily intended for search engines. Despite web crawlers working for a search engine, some web crawlers collect information from websites for SEO purposes such as site auditing and traffic analysis. Instead of offering search results to search engine users, they provide valuable information to website owners (like Alexa).
Since you have a basic idea of what a web crawler is, you might be wondering how a web crawler works.
There are a large number of web pages available on the internet and their number is increasing rapidly every day. How does a web crawler skim them all?
In fact, not all content on the Internet is indexed by web crawlers. Some pages are not open to search engine robots (#) and some simply do not have the opportunity to meet them.
Start from seed URLs
Normally, a web crawler starts its journey from a set of known URLs, or so-called seed URLs. He walks the Meta information web pages (e.g. title, description) as well as the body of the web page. As these pages are indexed, the crawler continues to crawl the hyperlinks to visit the web pages that are linked in the starting pages.
So here is the basic route a web crawler would take:
- Access the list of known web pages
- Extract the URLs that are linked in these web pages and add them to the list
- Keep visiting newly added pages
By constantly visiting web pages, web crawlers can discover new pages or URLs, update changes to existing pages, and flag those links as dead.
Web crawlers prioritize
Even though web crawlers are automated programs, they cannot keep pace with the rapid expansion of the Internet and constant changes in web pages. In order to capture the most relevant and valuable information, web crawlers need to follow certain rules that help prioritize all added links, which should be visited first.
- Web pages that are linked by many other relevant pages will be considered more informative than those pages without any reference. Web crawlers are more likely to prioritize visiting these web pages.
- Web crawlers revisit web pages to make sure they keep up with updates and get new information. A regularly updated webpage can be crawled more frequently than ones that rarely make changes.
All of these rules are made to help this whole process to be more efficient and to be more selected on the content they explore. The goal is to provide the best search results to search engine users.
A search index helps a search engine return results quickly and efficiently. It works like an index in a book – to help you quickly jump to the needed pages (information) with a list of keywords (or chapters).
The robot builds the index. It visits the pages of the website, collects the content, places it in an index and sends it to the database. You can think of the index as a huge database of words and corresponding pages where they appear.
For webmasters, it is important to ensure that the website is properly indexed. Only when the web page is indexed will it appear in search results and be discovered by the public. While a website owner can also decide how a search crawler crawls their website. Robots.txt is one such file that webmasters create to tell search bots how to crawl their pages.
As mentioned, the way a search engine crawls your website can affect how your pages are indexed and therefore whether they show up in search results. This is obviously what an SEO professional would care about.
If the ultimate goal is to get more traffic from a search engine like Google, there are a few steps you need to pay attention to:
Get Crawled: High Quality Backlinks
A web crawler bot starts from a list of seed URLs and these are normally quality pages from high authority websites. If the page you want to rank is linked by these pages, it will definitely be crawled by the bot. We don’t know what the starting URLs are, but you’re more likely to be crawled if you have more backlinks, especially when they come from high-performing websites.
In short, earning more backlinks to your website is essential, especially from relevant, high-quality pages.
Get indexed: original content
Your page can be crawled but not indexed. The web crawler bot is selective. It won’t store everything they’ve seen in the search index. There is a way to find out how many pages on your website are indexed by Google – type in “site:your domain” and do a Google search.
If you want to know exactly which pages are indexed and which are not, the data is available at Google Search Console: Google Search Console
So, what type of content is indexed (by Google for example)? Many influential factors come into play so the first thing to do is to write original content. Google’s mission is to provide valuable content to its users. It is almost the same for all search engines and duplicate content is always subject to penalties. Do research intent and keyword research. Write and tell your own story or opinion.
Sometimes web crawling and web scraping are used interchangeably. However, they are applied in very different scenarios for different purposes. Web crawling is a search engine crawler exploring unknown pages to store and index while web scraping is targeting a certain list of URLs or domains and extracting necessary data into files to find them. other uses.
Web scraping and web crawling work differently.
As we mentioned above, web crawling starts from a list of seed URLs and continues to visit what is linked to expand the reach to more unknown pages. Although a crawler may have a set of rules to decide which page to visit before others, it does not have a fixed list of URLs or is limited to a certain type of content.
However, web scraping has its clear target. (What is web scraping?) People come to web scraping with a list of URLs or domains and know exactly what data they are capturing from those pages.
For example, a shoe seller may wish to download information about shoe suppliers from Aliexpress, including supplier name, product specifications, and prices. A web scraper will visit the domain (Aliexpress), search for a keyword to get a list of relevant URLs, visit those pages and locate the necessary data on the HTML file and save it to a document.
They have different goals.
Web crawling consists of exploring and scrutinizing as many pages as possible, indexing those that are useful and storing them in the database in order to build an effective search engine.
A web scraper can work for very different purposes. People can use it to gather information for research, data for migrating from one platform to another, prices for competitor analysis, contacts for lead generation, and more.
They have one thing in common: they both rely on an automated program to make work (impossible for a human) doable.
If you are interested in web scraping and data extraction, there are several ways to get started.
Learn a programming language.
Python is widely used in web scraping. One reason is that open source libraries like Scrapy and BeautifulSoup are well built and mature to work on Python. Besides Python, other programming languages are also used for web scraping, such as Node.js, Php, C++.
Learning a language from scratch takes time and it’s good if you can start from what you know. If you are a beginner, evaluate your web scraping project better and choose a language that best suits your request.
Get started with a no-code or low-code web scraping tool.
It really takes time and energy to learn a programming language from scratch and be good enough to tackle a web scraping project. For a business or entrepreneurs busy maintaining a business, data services or a low-code web scraping tool is a better option.
The main reason is that it saves time. Since the launch of Octoparse in 2016, millions of users have used Octoparse to mine web data. They take advantage of the interactive workflow and intuitive tips guide to create their own scrapers. A low-code tool also enables team coordination as it lowers the threshold for processing web scraping and web data.
If you need to download web data, try Octoparse (free plan available). these webinars will get you on board and more importantly, if you get stuck, feel free to contact our support team ([email protected]). They will cover you.
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Article in Spanish: ¿Qué Es Web Scraping (Web Crawler) and Cómo Funciona?
Also can read the web scraping articles in el Official site