In this article, we will introduce web crawlers and examine how they work.
Surely you have searched many times on Google; But have you ever wondered, “How does Google know where to look?” The answer to this question is “web crawlers”. They can search the web and index it so you can easily find different items. In the following, we will fully explain this issue.
Search engines and crawlers
When you use a keyword in a search engine like Google or Bing, this website scans the trillions of pages to create a list of results related to that phrase. Here, questions arise in the minds of curious users: How exactly do these search engines access all of these pages? How do they know how to search for them and produce these results in a few seconds and show them to the user?
The answer to this question is web crawlers, also known as spiders. They are automated programs called robots or bots that crawl across the web to be added to search engines. These bots find various websites to generate a list of pages that will eventually appear in your search results.
Crawlers also create and store copies of these pages in the engine database, allowing you to quickly search for different items. For this reason, search engines often place cached versions of sites in their databases.
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 catalogs 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.
Website maps and selection
How do crawlers choose to crawl websites? We have to say that the most common scenario is that website owners want search engines to crawl their sites. They can achieve this by asking Google, Bing, Yahoo or another search engine to index their pages. This process varies from engine to engine. Also, search engines often select popular and convenient websites to crawl by tracking the number of times a URL links to other public websites.
Website owners can use special processes to help search engines index their websites; Like uploading a sitemap. This file contains all the links and pages that are part of your website. Also, this file is usually used to indicate which pages are to be indexed.
When search engines have already crawled a website, they will automatically re-select that website to do so. The number of times it will be done will vary depending on the popularity of the website and other criteria; Therefore, website owners often update their sitemaps.
Hide pages from crawlers
What if a website does not want some or all of its pages to appear in a search engine? For example, you may not want people to be able to search for a member-only page or see a 404 error page on your site. This is where the crawl deprivation list called robots.txt comes into play. This option is a simple text file that tells crawlers which web pages to remove from the index.
Another reason robots.txt is important is that web crawlers can have a significant impact on website performance. Because crawlers download virtually all of your web pages, they can slow you down. Also, their work does not have a predictable time and they enter without approval. If you do not need to crawl your pages frequently, stopping crawlers may help reduce some of your website load. Fortunately, most crawlers stop crawling on some pages according to the site owner’s rules.
Metadata Magic
Below the URL and title of each Google search result, you will find a brief description of the page. These explanations are called “snippets”. You may have noticed that the snippets of the pages on Google do not always match the actual content of the websites. This is because many websites have something called a “meta tag”. A meta tag is a custom description that website owners add to their pages.
Website owners often provide deceptive metadata descriptions that make you click on the website. Google also lists other metadata, such as prices and stock. This is especially useful for those who have e-commerce websites.
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
- Bingbot
- Slurp Bot
- DuckDuckBot
- Baiduspider
- Yandex Bot
- Sogou Spider
- Exabot
- Alexa Crawler
Your search
Web search is an essential part of using the Internet. Searching the web is a great way to discover new websites, stores, communities, and interests. Web crawlers visit millions of pages every day and add them to search engines. Finally, we must say that reptiles also have disadvantages; But they are also very valuable to website owners and visitors.