Surely, you have searched many times on Google; But have you ever wondered, "How does Google know where to search?" The answer to this question is "web crawlers". They can search the web and index it so you can find things easily. In the following, we will explain this issue completely.

Search engines and crawlers

When you search using a keyword in a search engine like Google or Bing, this website scans trillions of pages to generate a list of results for that term. Here, questions arise in the minds of curious users: How exactly do these search engines access all these pages? How do they know how to search for them and generate 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 the web to be added to search engines. These bots find different websites to generate a list of pages that will eventually appear in your search results.

Also, crawlers create and store copies of these pages in the engine's database, allowing you to quickly search for different ones. For this reason, search engines often include cached versions of sites in their databases.

Website maps and selection

How do crawlers choose websites to crawl? We must 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 appropriate websites to crawl by tracking how often a URL is linked on other public websites.

Website owners can use certain 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, the said 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 based on the popularity of the website and other criteria; Therefore, website owners update their sitemaps frequently.

Hide pages from crawlers

What if a website doesn't 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 members-only page or see your site's 404 error page. This is where the crawler exclusion list known as robots.txt comes into play. This option is a simple text file that tells crawlers which web pages to exclude from indexing.

Another reason why robots.txt is important is that web crawlers can have a significant impact on website performance. Since crawlers basically download all the pages of your website, they can slow things down. Also, their work has no predictable time and comes in without approval. If you don't need your pages to be indexed frequently, stopping crawlers may help reduce some of the load on your website. Fortunately, most crawlers stop crawling certain pages based on the site owner's rules.

The magic of metadata

Below the URL and title of each Google search result, you'll find a short description of the page. These descriptions are called "snippets". You may have noticed that the snippets of the pages in 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.