How Search Engines Work, Part One: Crawling and Indexing

February 15, 2023
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Most people today constantly rely on their smartphones. Want food? You can order through an app. Need conversions from metric to imperial? You can look it up through Google. The internet seems to have answers for everything, from immediate needs to entertainment and personal fulfillment. If you’re to leverage its capabilities, though, you need more than a surface knowledge of how it delivers information to people. If you want to know how to drive traffic to your website, you need to know more about the engine that enables this process!

Google, DuckDuckGo, Bing, and other search engines are tools that match a person’s search query to web content that addresses it. For example, if you type ‘restaurants near me,’ the search engine will return a list of websites and content, ranked by relevance aligned with the query. Here are other things that business owners and marketers should understand about search engines.

How Do Search Engines Work?

All search engines have two parts—an index and algorithms. The search index is a body of data that stores information about web pages. It is essentially a digital archive, and the links you see in search results pages are from the index. Meanwhile, search algorithms are computer programs that decide on the rankings of these results. 

All search engines want to provide the most relevant results for users. Theoretically, this practice is how they get market share. If many people find their services relevant, there will be more users of their search engine. Google has the largest market share at 92.24 percent, so understanding how it indexes and ranks data is vital if you want to rise in its SERPs.

How Does a Search Engine Create Revenue?

Since search engines provide a free service, you might be wondering how they earn money. Search providers get paid through pay-per-click advertising. Through this internet advertising model, search providers can charge advertisers a fixed price for every click their ads earn. These ads go on digital space that belongs to the company, so having a more significant market share is vital for search engines. With more users, there will be more ad clicks, which means higher revenues.

Why Learn about Search Engines?

Even if you don’t want to pay for advertising, it is important to know how search engines work. When you understand how search engines rank content, you will grow your website organically using relevant or competitive keywords.

Since Google has the most potential to send traffic to websites, it is the one that SEO professionals spend time understanding. Before you understand how an algorithm works, you must know what it takes to maintain a web index.

Building and Maintaining a Web Index

Knowing how Google retrieves and ranks information starts with understanding how it archives web pages. This process happens in four steps—discovery, crawling, processing, and indexing.

Discovering URLs

The first step is finding URLs to discover them. Google typically uses three ways to find URLs—backlinks, sitemaps, and URL submissions. Since Google has an existing index with trillions of pages, they can discover unindexed ones. The search engine can locate any page that links to a page in its index. Another way that it can find URLs is through sitemaps. A sitemap lists a website’s vital pages—if you submit it to Google, it could help them index your website quickly. Finally, Google also accepts individual submissions of URLs through the Google Search Console.

Crawling Pages

The next step, after discovering URLs, is crawling. Web crawling uses a bot, a computer program, to visit and download the pages it has found. Google queues crawls based on page rank, how old the page is, and how often the URL changes. If you have a large website, it will take a while for Google to crawl all of the pages.

Processing and Rendering

The third step after discovering and crawling is processing. When Google receives the data, it will try to understand and extract information from these pages. The exact process that the search engine uses is unknown to people outside Google. However, it is enough for website owners to know that Google extracts and stores content from links to process the pages. To fully process a page, Google needs to render it in its entirety and run the page code to see how it finds users. Processing can occur before and after Google renders HTML.

Indexing Pages

Once the algorithm fully understands what a page contains, it adds the data to the search index. When a Google user types a keyword or a search query, they are not going through the entire internet to find results. What happens is they search Google’s index of pages. If the page is not in the index, the search engine might not “find” it. So, website owners need to submit their pages to Google and other engines like Bing.


Understanding how search engines work is essential for website owners or marketers. Since most people look up information through Google, Bing, and other search engines, your web page needs to be part of their index for users to find it. Otherwise, you would need to manually direct people to your domain, which isn’t ideal for any website owner who wants to scale their growth. Even if you’re focusing on an organic search strategy, it pays to know how Google chooses what links are relevant and which ones to push up in search results pages.

Read Part Two of our series on how search engines work, where we go into detail about how Google and other search engines rank pages.

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